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^RINCiP^ES 

V  HITMAN 


fiAVJS 


TRACTOR  PRINCIPLES 


TRACTOR  PRINCIPLES 

THE  ACTION,  MECHANISM,  HANDLING, 
CARE,  MAINTENANCE  AND  REPAIR 
OF  THE  GAS  ENGINE  TRACTOR 


BY 

ROGER  B.  WHITMAN 


ENGINE  PRINCIPLES,"  "MOTOB-CTCLH 
PRINCIPLES,"  ETC. 


FULLY  ILLUSTRATED 


D.  APPLETON  AND  COMPANY 

NEW  YORK  LONDON 

1920 


LT 

UNIVERSITY 


COPYRIGHT,   1920,  BY 

D.  APPLETON  AND  COMPANY 


IK   TH«  UK1TE)  STATBS  O»   AMERICA 


FOREWORD 

The  tractor  of  to-day  is  built  in  almost  as  many 
types  and  designs  as  there  are  tractor  makers,  and  is 
far  from  being  as  standard  as  the  automobile.  There 
are  tractors  with  one  driving  wheel,  with  two  driving 
wheels,  with  three  and  with  four,  as  well  as  three 
arrangements  of  the  crawler  principle;  there  are  two- 
wheelers,  three-wheelers  and  four-wheelers;  tractors 
that  are  controlled  by  pedals  and  levers  and  tractors 
that  are  driven  by  reins. 

Thus  if  a  man  who  is  competent  to  handle  and 
care  for  one  make  is  given  another  make  to  run,  he 
may  be  entirely  at  a  loss  as  to  how  it  works  and  how 
it  should  be  handled. 

It  is  the  purpose  of  this  book  to  explain  and  de- 
scribe all  of  the  mechanisms  that  are  in  common  use 
in  tractor  construction,  to  the  end  that  the  reader 
may  be  able  to  identify  and  understand  the  parts  of 
whatever  make  he  may  see  or  handle. 


CONTENTS 
CHAPTER  I 

TRACTOR  PRINCIPLES 

Comparison  between  tractors  and  automobiles — What 
is  required  for  each — Advantage  of  understanding 
the  mechanism — No  standard  tractor  design — Prin- 
cipal parts  of  a  tractor — Necessity  for  each  .  . 

CHAPTER  II 

ENGINE  PRINCIPLES 

Power  attained  from  heat — Combustible  mixture — 
Principle  of  engine  operation — Combustion  space — 
Gas  engine  cycle — Dead  strokes — Flywheel— Start- 
ing an  engine — Inlet  stroke — Compression  stroke — 
Importance  of  compression — Ignition — Advance 
and  retard  of  ignition — Power  stroke — Exhaust 
stroke — Production  of  power — Vertical  and  hori- 
zontal engines — Firing  order 

CHAPTER  III 

ENGINE  PARTS 

Base  —  Bearings  —  Cylinders  —  Crankshaft  —  Piston 
— Connecting  rod  —  Wrist  pin  —  Piston  rings — 
Valves — Cam — Valve  mechanisms — Cooling  sys- 
tem   

CHAPTER  IV 

FUELS  AND  CARBURETION 
Oxygen  necessary  for  combustion — Forming  a  mixture 
— Rich  and  poor  mixtures — Carbon — Preigniti^n — 
vii 


viii  CONTENTS 

FAQB 

Carbureter — Spray  nozzle — Evaporation  of  fuels — 
Carbureter  principles — Extra  air  inlet — Effect  of 
heat  on  mixture — Loading — Strangler  ....  52 

CHAPTER  V 

CARBURETERS 

Carbureter  parts — Manifold — Action  of  carbureter — 
Float  feed — Kerosene  and  gasoline — Descriptions 
of  carbureters — Pump  feed — Use  of  water  in  the 
mixture — Application  of  heat — Fuel  pumps — Air 
cleaners — Governors 70 

CHAPTER  VI 

IGNITION 

Principle  of  ignition — Point  of  ignition — Preignition — 
Advance  and  retard — Parts  of  ignition  system — 
Magnetism — Induction — Magneto — Action  of  ar- 
mature— Armature  windings — Circuit  breaker — 
Circuit — Shuttle  and  inductor  armatures  —Sparking 
current — Grounded  circuit — Magneto  parts — Im- 
pulse starter 102 

CHAPTER  VII 

BATTERY  IGNITION  SYSTEMS 

Principle  of  spark   coil — Windings — Timer — Atwater- 

Kent  system — Vibrator — Spark  plugs     ....     131 

CHAPTER  VIII 

TRANSMISSION 

Transmission  parts — Clutches — Necessity  for  change 
speed  gear — High  and  low  gear — Types  of  change 
speed  gears — Necessity  for  differential — Principle 
of  differential — Drives — Worm  .  .  .  143 


CONTENTS  ix 


PAGE 

CHAPTER  IX 

TRACTOR  ARRANGEMENT 

Tractor  requirements — Tractor  types — Engine  position 

— Front  axles — Spring  supports 167 

CHAPTER  X 

LUBRICATION 

Importance  of  lubrication — Effect  of  oil — Kinds  of  oil — 
Effect  of  temperature  on  oil — Using  the  right  kind 
of  oil  —  Burning  point  —  Viscosity  —  Lubrication 
charts — Oiling  systems — Oil  pumps — Mechanical 
oiler — Oil  cup — Grease  cup 175 

CHAPTER  XI 

TRACTOR   OPERATION 

Using  a  new  tractor— Breaking  in — Daily  inspection — 
Driving — Shifting  gears — Driving  on  hills — Using 
the  engine  as  a  brake — Cold  weather  conditions — 
Starting  in  cold  weather — Protection  against  freez- 
ing— Starting  a  tractor 201 

CHAPTER  XII 

ENGINE  MAINTENANCE 

Fuel  system  and  carbureter — Carbureter  adjustment — 
Dirt  in  the  fuel — Running  on  kerosene — Care — 
Magneto  and  ignition  system — Care  of  magneto — 
Smoothing  platinum  points — Adjustment — Timing 
a  magneto — Testing  a  magneto — Ignition  trouble — 
Compression — Testing  for  compression  leaks — 
Valve  grinding — Valve  timing — Carbon — Remov- 
ing carbon 213 


x  CONTENTS 

PAOB 

CHAPTER  XIII 

LOCATING  TROUBLE 

Engine  will  not  start — Engine  loses  power — Engine 
stops — Engine  misses — Engine  starts;  but  stops — 
Engine  overheats — Engine  smokes 246 

CHAPTER    XIV 

CAUSES  OF  TROUBLE 
Troubles  and  their  causes  in  tabular  form     ....     259 


ILLUSTRATIONS 


Principle  of  er^a  air  LL>. 


xii  ILLUSTRATIONS 


25  "  Kingston  "carburetor,  dual  model  .     ...  77 

26  "E-B"  carburetor        ........  79 

27  "E-B"  carburetor,  side  view  ......  81 

28  Pump-fed  carburetor    ........  82 

29  "Titan"  carburetor      ........  84 

30  Pump-fed  carburetor  with  two  fuel  nozzles  .     .  85 

31  "Hart-Parr  "mixture  heater  ......  87 

32  "Twin  City  "manifold      .......  88 

33  Fuel  pump   ...........  90 

34  "Avery"  fuel  connections       ......  92 

35  "  Oil  Pull"  fuel  system      .......  93 

36  Air  washer    ...........  95 

37  Air  strainer  ...........  96 

38  "E-B  "governor     .........  97 

39  "Case  "governor    .........  98 

40  "Hart-Parr"  governor       .......  99 

41  Vertical  governor    .........  101 

42  Armature     ...........  107 

43  Flow  of  magnetism  through  armature  core  .     .  108 

44  One  complete  revolution  of  the  armature     .     .  Ill 

45  Connections  of  Bosch  magneto     .....  112 

46  "K-W"  inductor    .........  115 

47  "K-W"  inductor  in  three  positions  ....  117 

48  "Dixie  "inductor    .........  118 

49  Three  positions  of  "Dixie"  inductor       ...  120 

50  "Bosch"  circuit  breaker    .......  121 

51  "K-W  "circuit  breaker     .......  122 

52  "Bosch"  magneto  in  section  ......  126 

53  "K-W  "magneto  in  section    ......  129 

54  Magnetism  in  a  copper  wire   ......  132 

55  Magnetism  from  electricity     .....    {.  133 


ILLUSTRATIONS  xiii 


FIG. 


56  Principle  of  spark  coil 134 

57  "Atwater-Kent"  ignition  system       ....  136 

58  Vibrator  coil  ignition  system 139 

59  Sparkplug 141 

60  Internal  clutch 144 

61  Plate  clutch 147 

62  Principle  of  sliding  gear 155 

63  Principle  of  jaw  clutch  change  speed  gear    .      .  157 

64  "I.  H.  C."  chain  drive,  showing  differential      .  162 

65  "Case  "rear  axle 163 

66  "Oil  Pull "  rear  axle 164 

67/  Driving  worm 165 

68  Tractor  arrangement 168 

69  Tractor  arrangement 169 

70  "Gray  "tractor 171 

71  Types  of  front  axles 172 

72  Spring  support 173 

73  "Mogul"  oiling  diagram 180 

74  "Illinois  "oiling  diagram 183 

75  End  of  "Twin  City"  connecting  rod       ...  185 

76  Wrist  pin  lubrication 186 

77  Force  feed  oiling  system  of  "Gray"  engine       .  187 

78  Oil  pump 188 

79  "E-B"  oil  pump 189 

80  Oil  pump  with  hollow  plunger 190 

81  Methods  of  preventing  oil  leaks 191 

82  "Titan"  lubricator 192 

83  "I.  H.  C."  method  of  oiling  crank  pins        .     .  193 

84  "Hart-Parr  "oiling  system 194 

85  Oil  cup 195 

86  Proper  use  of  a  grease  cup 196 


xiv  ILLUSTRATIONS 

no.  PAGE 

87  "Titan "10-20  oiling  diagram 198 

88  "International"  oiling  diagram 199 

89  Grinding  valve  in  engine  with  fixed  head     .     .231 

90  Grinding  valve  in  detachable  head    ....  233 

91  Grinding  valve  in  detachable  seat     ....  234 

92  Valve  seat  cutter 235 

93  "Holt  "valve  arrangement 236 

94  Valve  timing,  using  marks  on  flywheel  .     .     .  238 

95  Valve  timing 239 

Index  261 


TRACTOR  PRINCIPLES 


TRACTOR  PRINCIPLES 

CHAPTER  I 

TRACTOR  PRINCIPLES 

WHILE  tractors  and  automobiles  are  the 
same  in  general  principles,  there  is  a  wide 
difference  between  them  in  design,  construc- 
tion, and  handling,  due  to  the  differences  in 
the  work  that  they  do  and  in  the  conditions 
under  which  they  do  it. 

An  automobile  is  required  to  move  only 
itself  and  the  load  that  it  carries.  While  it 
can  run  over  rough  roads,  these  must  be 
hard  enough  to  support  it ;  on  soft  ground  it 
will  sink  in  and  be  unable  to  get  itself  out. 
It  can  make  great  speed  over  smooth,  level 
roads;  but  only  rarely  do  road  and  police 
conditions  permit  it  to  run  its  fastest  for 

more  than  a  few  minutes  at  a  time.    For  the 

l 


2  TRACTOR  PRINCIPLES 

greater  part  of  its  life  it  develops  only  a  por- 
tion of  the  power  of  which  it  is  capable. 

A  tractor,  on  the  other  hand,  is  intended 
not  to  carry,  but  to  haul.  It  must  run  and 
do  its  work  on  rough  hillsides,  soft  bottoms, 
or  any  other  land  where  it  is  required  to  go. 
Instead  of  developing  speed  it  develops  pull- 
ing power,  and  must  be  able  to  develop  its 
full  power  continuously. 

Appearance  and  comfort  count  for  a  great 
deal  in  an  automobile,  and  much  attention 
is  devoted  to  making  it  noiseless  and  simple 
to  manage.  These  things  do  not  apply  in  a 
tractor,  which  is  a  labor-saving  and  money- 
making  machine,  valuable  only  for  the  work 
that  it  can  do.  There  is  no  question  of  up- 
holstery or  nickel-plating;  all  that  is  wanted 
is  a  machine  that  will  do  the  required  work 
with  the  least  possible  cost  of  operation. 

As  is  the  case  with  any  kind  of  machine 
that  is  purchased  as  a  money-maker,  its  cost 
should  be  as  low  as  is  consistent  with  its 
ability  to  do  its  work.  Any  extra  cost  for 


TRACTOR  PRINCIPLES  3 

accessories,  or  finish,  or  other  detail,  is 
wasted  unless  it  permits  the  machine  to  do 
more  work,  or,  by  making  the  operator  more 
comfortable,  allows  him  to  run  the  machine 
for  a  longer  stretch  of  time  or  with  greater 
efficiency. 

It  may  be  taken  for  granted  that  any 
tractor  will  rum  and  will  do  its  work  with 
satisfaction,  provided  it  is  sensibly  handled 
and  cared  for.  Far  more  troubles  and  break- 
downs come  from  careless  handling  and  from 
neglect  than  from  faulty  design  and  material. 
A  tractor  that  is  running  and  doing  its  work 
is  earning  a  return  on  the  money  invested  in 
it ;  when  it  is  laid  up  for  repairs  there  is  not 
only  a  loss  of  interest  on  the  investment,  but 
a  loss  of  the  value  of  the  work  that  it  might 
be  doing. 

To  keep  a  tractor  running  is  a  matter  only 
of  understanding  and  of  common  sense ;  com- 
mon sense  to  realize  that  any  piece  of  ma- 
chinery needs  some  degree  of  care  and  atten- 
tion, and  understanding  of  where  the  care 


4  TRACTOR  PRINCIPLES 

and  attention  should  be  applied.  The  more 
thoroughly  a  tractor  operator  understands 
his  machine,  the  more  work  he  will  be  able  to 
get  out  of  it,  and  the  more  continuously  it  will 
run.  This  is  only  another  way  of  saying  that 
understanding  and  knowledge  pay  a  direct 
return  in  work  done  and  money  earned. 

In  the  early  days  of  the  automobile  there 
were  as  many  types  of  cars  as  there  were 
manufacturers.  As  time  has  gone  on,  the 
unsatisfactory  ideas  have  been  weeded  out, 
and  automobiles  have  approached  what  may 
be  called  a  standard  design. 

At  the  present  time,  tractor  designs  are 
varied,  and  it  is  hardly  possible  to  speak  of 
any  type  as  standard.  The  reason  for  this 
lies  in  the  fact  that  many  manufacturers 
start  with  a  design  for  one  special  part,  and 
build  the  tractor  around  it. 

For  example,  a  manufacturer  may  develop 
a  method  of  driving  the  wheels  that  he  feels 
is  especially  good  for  tractor  work.  In  ap- 
plying it  he  may  find  that  the  engine  must  be 


TEACTOE  PEINCIPLES  5, 

so  placed  on  the  frame  that  when  the  power, 
pulley  is  in  position  the  belt  will  interfere 
with  the  front  wheels  unless  they  are  small ; 
he  therefore  uses  small  front  wheels,  and  ad- 
vocates them  for  tractors. 

Another  manufacturer  with  a  patent  steer- 
ing gear  may  be  able  to  place  the  power  pul- 
ley so  that  there  is  ample  clearance  for  the 
belt ;  he  finds  that  by  using  high  front  wheels 
he  can  get  a  better  support  for  the  frame, 
and  therefore  claims  that  high  front  wheels 
are  an  advantage. 

Other  designs  may  be  based  on  having 
three  wheels,  or  two ;  advantages  are  claimed 
for  each  type,  and  each  type  undoubtedly 
has  them. 

The  selection  of  a  tractor  is  based  on  one's 
own  experience  or  on  that  of  neighbors,  or  on 
the  ability  of  the  salesman  to  bring  out  the 
advantages  of  the  make  that  he  sells;  but 
when  the  tractor  is  bought  and  delivered,  its 
ability  to  do  the  work  promised  for  it  de- 


6  TRACTOR  PRINCIPLES 

pends  solely  on  the  care  with  which  it  is 
handled  and  looked  after. 

Whatever  the  design  of  a  tractor  may  be, 
there  are  certain  parts  that  it  must  have  in 
order  to  do  the  work  required  of  it.  These 
parts,  or  groups  of  parts,  are  as  follows : 

Engine.— This  furnishes  the  power  by 
which  the  tractor  operates. 

Clutch.— By  means  of  a  clutch  the  engine 
may  be  connected  with  the  mechanism,  so  that 
the  tractor  moves,  or  it  may  be  disconnected, 
so  that  it  may  run  without  moving  the  trac- 
tor. 

Change  Speed  Gear.— As  will  be  explained 
in  later  chapters,  an  engine,  in  order  to  work 
most  efficiently,  should  run  at  a  fixed  speed; 
the  tractor  should  be  able  to  run  fast  or  slow, 
according  to  conditions.  A  change  speed 
gear  is  therefore  provided,  by  which  the  speed 
of  the  tractor  may  be  changed,  although 
there  is  no  change  in  the  speed  of  the  en- 
gine. 

Drive.— The  drive  is  the  mechanism  that 


TRACTOR  PRINCIPLES  7 

applies  the  power  of  the  engine  to  the  wheels, 
and  makes  them  turn. 

Differential.— When  a  tractor  makes  a 
turn,  the  outside  wheels  cover  a  larger  cir- 
cle than  the  inside  wheels,  and  therefore  must 
run  faster  in  order  to  get  around  in  the  same 
time.  It  is  usually  the  case  that  the  power 
of  the  engine  is  applied  to  both  driving 
wheels;  if  both  were  solid  on  the  axle,  like 
the  wheels  of  a  railroad  car,  one  would  be 
forced  to  sh'p  when  making  a  turn,  which 
would  waste  power.  By  applying  a  differ- 
ential, the  engine  can  drive  both  wheels,  but 
the  wheels  may  run  at  different  speeds  when 
conditions  require  it. 

The  clutch,  change  speed  gear,  drive  and 
differential  form  the  transmission. 

Steering  gear.— By  means  of  the  steering 
gear  the  direction  in  which  the  tractor  moves 
may  be  changed. 

Supports.— A  tractor  moves  on  broad-tired 
wheels,  or  on  crawlers,  which  are  so  formed 
that  they  grip  the  ground  and  do  not  sh'p. 


8  TEACTOE  PEINCIPLES 

They  give  so  broad  a  support  that  even  on 
soft  ground  the  weight  of  the  tractor  will 
not  pack  the  soil  sufficiently  to  injure  it  as 
a  seed  bed. 

Frame.— The  frame  is  the  foundation  of 
the  tractor,  and  holds  the  parts  in  the  proper 
relation  to  each  other.  It  is  usually  made  of 
channel  steel,  the  parts  being  bolted  to  it; 
in  some  tractors,  however,  the  parts  are  so 
attached  to  each  other  that  they  form  their 
own  support,  and  no  other  frame  is  needed. 

Tractor  manufacturers  make  these  parts  in 
different  ways;  all  accomplish  the  same  re- 
sult, but  do  it  by  different  methods.  The 
main  principles  are  much  the  same,  and 
should  be  known  and  understood.  They  are 
described  and  explained  in  the  succeeding 
chapters. 


CHAPTER  II 

ENGINE  PRINCIPLES 

THE  working  paijt  of  a  tractor  is  the  en- 
gine; it  is  this  that  furnishes  the  power  that 
makes  the  machine  go. 

The  engine  gets  its  power  from  the  burn- 
ing of  a  mixture  of  fuel  vapor  and  air. 
When  this  mixture  burns,  it  becomes  heated, 
and,  as  is  usual  with  hot  things,  it  tries  to 
expand,  or  to  occupy  more  room. 

The  mixture  is  placed  in  a  cylinder,  be- 
tween the  closed  end  and  the  piston ;  it  is  then 
heated  by  being  burned,  and,  in  struggling 
to  expand,  it  forces  the  piston  to  slide  down 
the  cylinder.  This  movement  of  the  piston 
makes  the  crank  shaft  revolve,  which  in  turn 
drives  the  tractor. 

The  first  step  in  making  the  engine  run  is 
to  put  a  charge  of  mixture  into  the  cylinder, 


10  TRACTOR  PRINCIPLES 

and  it  is  clear  that  if  the  burning  of  the 
charge  is  to  move  the  piston,  the  piston  must 
be  in  such  a  position  that  it  is  able  to  move. 
When  the  mixture  is  burned,  the  piston  must 
therefore  be  at  the  closed  end  of  the  cylinder. 

After  the  charge  of  mixture  has  been 
burned,  the  cylinder  must  be  cleared  of  the 
dead  and  useless  gases  that  remain,  in  or- 
der to  make  room  for  a  fresh  charge. 

The  charge  of  mixture  is  drawn  into  the 
cylinder  just  as  a  pump  sucks  in  water.  At 
a  time  when  the  piston  is  at  the  closed  end 
of  the  cylinder,  a  valve  is  opened  connecting 
the  space  above  the  piston  with  the  device 
that  forms  the  mixture ;  then  by  moving  the 
piston  outward,  mixture  is  sucked  into  the 
space  above  it.  When  the  piston  reaches  the 
end  of  its  stroke  the  cylinder  has  been  filled 
with  mixture,  and  the  valve  then  closes. 

It  would  be  useless  to  set  fire  to  the  mix- 
ture at  that  time,  for  the  piston  is  as  far 
down  the  cylinder  as  it  can  be,  and  pressure 
could  not  move  it  any  farther.  To  get  the 


ENGINE  PRINCIPLES  11 

piston  into  such  a  position  that  the  expand- 
ing mixture  can  move  it,  it  is  forced  back  to 
the  closed  end  of  the  cylinder.  This  squeezes 
or  compresses,  the  cylinderful  of  mixture 
into  the  small  space,  called  the  combustion 
chamber,  between  the  piston  and  the  cylinder 
head. 

If  the  mixture  is  now  burned,  the  piston 
can  move  the  length  of  the  cylinder,  and  in 
so  doing  it  develops  power. 

The  cylinder  is  cleared  of  the  burned  and 
useless  gases  by  opening  a  valve  and  push- 
ing them  out  by  moving  the  piston  back  to 
the  inner  end  of  the  cylinder.  When  this  has 
been  done,  the  valve  is  closed,  and,  by  open- 
ing the  inlet  valve  and  moving  the  piston 
outward,  a  fresh  charge  is  sucked  in,  and  the 
several  steps  of  the  gas  engine  cycle  are  re- 
peated. 

The  name  cycle  is  given  to  any  series  of 
steps  or  events  that  must  be  gone  through  in 
order  that  a  thing  may  happen.  Thus  the 
empty  shell  must  be  taken  out  of  a  gun  and 


12  TKACTOE  PRINCIPLES 

a  fresh  cartridge  put  in  before  the  gun  can 
be  fired  again,  and  that  series  of  steps  might 
be  called  the  gun  cycle. 

The  gas  engine  cycle  requires  the  piston 
to  make  four  strokes.  An  outward  stroke 
sucks  in  a  charge  of  mixture,  and  an  inward 
stroke  returns  the  piston  to  the  firing  posi- 
tion and  compresses  the  charge.  Then  comes 
the  outward  stroke  when  the  piston  moves 
under  power,  followed  by  the  inward  stroke 
that  clears  the  cylinder  of  the  burned  gases. 

For  every  stroke  of  the  piston  the  crank 
shaft  makes  a  half -revolution ;  the  crank 
shaft  therefore  makes  two  revolutions  to  four 
strokes  of  the  piston  and  to  each  repetition 
of  the  gas  engine  cycle. 

Of  these  four  strokes  of  the  piston 
only  one  produces  power.  The  other  three 
strokes,  called  the  dead  strokes,  are  required 
to  prepare  for  another  power  stroke. 

A  gas  engine  cylinder  thus  produces  power 
for  only  one  quarter  of  the  time  that  it  runs. 
This  is  one  of  the  striking  differences  be- 


ENGINE  PRINCIPLES  13 

tween  the  gas  engine  and  the  steam  engine, 
for  the  piston  of  a  steam  engine  moves  under 
power  all  of  the  time  that  the  engine  runs. 

A  one-cylinder  gas  engine  must  have  some- 
thing to  make  the  piston  go  through  the  dead 
strokes,  for  otherwise  the  piston  would  stop 
at  the  end  of  the  power  stroke ;  the  piston  is 
kept  in  motion  by  heavy  flywheels  attached 
to  the  crank  shaft.  These,  like  any  object, 
try  to  continue  in  motion  when  once  they  are 
started ;  a  power  stroke  starts  the  crank  shaft 
revolving  and  its  flywheels  keep  it  going. 

Thus,  the  piston  drives  the  crank  shaft 
during  the  power  stroke,  and  the  crank  shaft 
drives  the  piston  during  the  dead  strokes. 

To  start  an  engine,  the  crank  shaft  is  re- 
volved to  make  the  piston  suck  in  a  charge  of 
mixture  and  compress  it;  then  the  charge  is 
burned,  the  power  stroke  takes  place,  and 
the  engine  runs. 

A  clear  idea  of  what  goes  on  inside  of  the 
cylinder  is  quite  necessary  in  order  to  take 
proper  care  of  an  engine  and  to  get  the  best 


14  TEACTOE  PEINCIPLES 

work  out  of  it.  The  following  description 
applies  to  any  cylinder,  for  the  action  in  all 
cylinders  of  an  engine  is  the  same. 

Inlet  Stroke.— During  the  inlet  stroke  (No. 
1,  Fig.  1),  the  piston  moves  outward;  the  in- 
let valve  is  open,  and  the  exhaust  valve  is 
closed.  This  movement  of  the  piston  creates 
suction,  and  if  there  are  leaks  in  the  cylin- 
der, air  will  be  sucked  in  and  will  spoil  the 
proportions  of  the  charge.  This  will  prevent 
the  proper  burning  of  the  mixture,  and  the 
engine  will  lose  power. 

The  piston  moves  at  such  high  speed  that 
the  mixture  cannot  enter  fast  enough  to  keep 
up  with  it;  mixture  is  still  flowing  in  when 
the  piston  reaches  the  end  of  its  stroke,  and 
even  when  it  begins  to  move  inward  on  the 
next  stroke.  The  more  mixture  there  is  in 
the  cylinder,  the  more  powerfully  the  engine 
will  run;  the  inlet  valve  is  therefore  held 
open  for  as  long  a  time  as  the  mixture  con- 
tinues to  enter. 

In  slow-speed  1-cylinder  and  2-cylinder  en- 


INLET  OPEN 


V*     '  *     O 

>^LE^ 


BOTH  CLOSED' 

^ 

i69/3cr 
jormsp 


earn  CLOSED 


EXhA&SE 


PIG.  1. — THE  GAS  ENGINE  CYOUB 
15 


16  TRACTOR  PRINCIPLES 

gines  the  valve  closes  when  the  piston  reaches 
the  end  of  its  stroke;  on  high-speed  engines 
the  valve  does  not  close  until  the  piston  has 
moved  %  inch  or  y2  inch  on  the  compression 
stroke. 

Compression  Stroke.— During  the  compres- 
sion stroke  (No.  2,  Fig.  1)  the  piston  moves 
inward,  and  both  valves  are  closed.  This 
movement  places  the  piston  in  position  to 
move  outward  on  the  power  stroke.  As  the 
outlets  to  the  cylinder  are  closed,  the  charge 
of  mixture  cannot  escape,  and  is  therefore 
compressed  into  the  space  between  the  piston 
and  the  cylinder  head  when  the  piston  is  at 
the  inner  end  of  its  stroke.  This  space  is 
usually  about  one  quarter  the  volume  of  the 
cylinder;  the  charge  is  therefore  compressed 
to  about  one  quarter  of  its  original  volume. 

This  compression  of  the  charge  is  very  im- 
portant in  the  operation  of  the  gas  engine, 
and  any  interference  with  it  will  make  the 
engine  run  poorly. 

In  the  first  place,  it  improves  the  quality 


ENGINE  PEINCIPLES  17 

of  the  charge,  and  makes  it  burn  very  much 
better.  When  the  charge  enters  the  cylinder, 
the  fuel  vapor  and  air  are  not  thoroughly 
mixed;  much  of  the  fuei  is  not  turned  into 
vapor.  By  compressing  the  charge  it  be- 
comes heated;  this  vaporizes  the  fuel,  and 
vapor  and  air  become  thoroughly  mixed. 

Compression  also  increases  the  power. 
Suppose  that  the  cylinder  contains  a  quart 
of  mixture  which,  when  heated,  will  expand 
to  a  gallon.  If  this  quart  of  mixture  is  com- 
pressed to  a  half  pint,  it  will  not  lose  its  abil- 
ity to  expand  to  a  gallon,  and  will  exert  more 
pressure  in  expanding  from  a  half  pint  to  a 
gallon  than  from  a  quart  to  a  gallon. 

A  leaky  cylinder  will  cause  a  further  loss 
of  power  because  some  of  the  charge  will  es- 
cape during  the  compression  stroke,  which 
will  leave  less  to  be  burned  and  to  develop 
power. 

Ignition.— Setting  fire  to  the  charge  of  mix- 
ture is  called  the  ignition  of  the  charge,  and 
it  takes  place  close  to  the  end  of  the  com- 


18  TRACTOR  PRINCIPLES 

pression  stroke.  To  get  the  greatest  power, 
all  of  the  mixture  should  be  on  fire  and 
heated  most  intensely  as  the  piston  begins  the 
power  stroke. 

When  the  mixture  is  set  on  fire,  it  does  not 
explode  like  gunpowder,  but  burns  compara- 
tively slowly;  the  charge  is  ignited  by  an 
electric  spark,  and  the  flame  spreads  from 
that  point  until  it  is  all  on  fire.  In  order  to 
give  the  flame  time  to  spread,  the  spark 
passes  sufficiently  before  the  end  of  the  com- 
pression stroke  to  have  the  entire  charge  on 
fire  as  the  power  stroke  begins.  This  is 
called  the  advance  of  the  ignition. 

The  flame  takes  the  same  time  to  spread 
through  the  charge  when  the  engine  is  run- 
ning fast  as  when  it  is  running  slow.  There- 
fore if  the  engine  is  speeded  up,  the  spark 
must  be  advanced,  for  otherwise  the  piston 
would  be  on  the  power  stroke  before  the  flame 
would  have  time  to  spread  all  through  the 
mixture. 

When  the  engine  is  slowed  down,  the  spark 


ENGINE  PRINCIPLES  19 

must  have  less  advance,  or  must  be  retarded, 
for,  if  it  were  not,  the  charge  would  all  be  in 
flame,  and  exerting  its  full  pressure,  before 
the  piston  reached  the  end  of  its  compres- 
sion stroke. 

The  subject  of  ignition,  which  is  of  great 
importance,  is  covered  more  fully  in  Chap- 
ter VI. 

Power  Stroke.— During  the  power  stroke 
(No.  3,  Fig.  1)  the  piston  moves  outward,  and 
both  valves  are  closed.  As  it  begins,  the  mix- 
ture is  all  on  fire,  and  great  pressure  is 
exerted  against  the  piston. 

As  the  piston  moves  outward  the  combus- 
tion space  becomes  larger,  and  the  gases  ob- 
tain the  room  for  expansion  that  they  seek. 
As  they  expand,  the  pressure  that  they  ex- 
ert becomes  less.  By  the  time  the  piston  is 
three  quarters  the  way  down  the  power 
stroke,  the  pressure  is  so  reduced  that  it  has 
little  or  no  effect;  the  gases  are  still  trying 
to  expand,  however,  so  the  exhaust  valve  is 


20  TRACTOR  PRINCIPLES 

opened  at  that  point,  and  they  begin  to  es- 
cape. 

Exhaust  Stroke.— During  the  exhaust 
stroke  (No.  4,  Fig.  1)  the  piston  moves  in- 
ward and  the  exhaust  valve  is  open.  This 
movement  of  the  piston  pushes  the  burned 
gases  out  of  the  cylinder,  and  it  is  clear  that 
the  more  thoroughly  the  cylinder  is  emptied 
of  them,  the  more  room  there  will  be  for  a 
fresh  charge. 

In  high-speed  engines  the  gases  cannot  es- 
cape as  fast  as  the  piston  moves;  they  are 
still  flowing  out  when  the  end  of  the  stroke 
is  reached.  Therefore  the  valve  is  closed, 
not  at  the  end  of  the  stroke,  but  when  the 
piston  has  moved  about  %  inch  outward  on 
the  inlet  stroke.  The  inlet  valve  opens  as 
the  exhaust  valve  closes. 

It  can  be  seen  that  through  the  inlet  and 
compression  strokes  a  leak  will  reduce  the 
charge  and  so  interfere  with  the  production 
of  full  power.  The  piston  must  make  a  tight 
fit  in  the  cylinder,  the  valves  must  seat 


ENGINE  PRINCIPLES 


21 


tightly,  and  gaskets  and  other  parts  must  be 
in  proper  condition. 

Figure  2  shows  a  power  diagram  for  a 
1-cylinder  engine,  in  which  the  crank  shaft 


JL 


15T 
RF.V 

p  D 

REV 

1    CYL.1 

!|C 

P 

E 

CYLINDER  ENGINE:. 
ONE  POWLR  STROKE: 

CVCRYTWO  RLVOLUTIONS 
FIG.  2. — 1 -CYLINDER  POWER  DIAGRAM 


moves  under  power  during  one  stroke  out  of 
every  four.  An  engine  with  two  cylinders  can 
be  built  so  that  first  one  cylinder  applies 
power  and  then  the  other,  in  which  case  the 


22 


TRACTOR  PRINCIPLES 


crank  shaft  moves  under  power  during  two 
strokes  out  of  every  four. 
Figure  3  is  a  power  diagram  of  an  engine 


1 

2 

•• 

• 

- 

_n n_ 


lbf 
REV 

2° 
RQ/ 

CYL.l 

I 

C 

P 

E 

CYL.2 

P 

L 

I 

C 

2-CYL.  VERTICAL 

360°SHAFT 

FIG.  3.— 2-CYLiNDEE  POWER  DIAGRAM 

of  this  sort.  If  piston  1  is  moving  down  un- 
der power,  piston  2  is  also  moving  down,  but 
on  the  inlet  stroke.  The  following  stroke  is 
exhaust  in  cylinder  1  and  compression  in  cyl- 


ENGINE  PBINCIPLES  23 

inder  2,  and  cylinder  2  will  then  deliver  a 
power  stroke  while  cylinder  1  is  on  inlet. 
Thus  the  crank  shaft  will  Deceive  a  power 
stroke,  followed  by  a  dead  stroke;  then  an- 
other power  stroke  and  another  dead  stroke, 
and  so  on. 

There  will  be  the  disadvantage,  however, 
that  the  pistons,  moving  up  and  down  to- 
gether, will  cause  vibration,  which  in  the 
course  of  time  will  be  likely  to  give  trouble. 
To  overcome  this,  a  2-cylinder  engine  can  be 
built  as  indicated  in  Figure  4. 

In  this  engine  the  cranks  project  on  op- 
posite sides  of  the  crank  shaft  instead  of  on 
the  same  side,  as  in  Figure  3;  the  pistons 
thus  move  in  opposite  directions,  and  pro- 
duce no  vibration.  Power  will  be  unevenly 
applied,  however,  for  both  power  strokes  oc- 
cur in  one  revolution,  with  two  dead  strokes 
in  the  succeeding  revolution. 

With  piston  1  moving  down  on  power,  pis- 
ton 2,  moving  upward,  can  only  be  perform- 
ing compression  or  exhaust.  If  it  is  on  com- 


24 


TRACTOR  PRINCIPLES 


_n 


ur 


pr 

REV 

2D 
REV. 

CYL.1 

I 

C 

P 

E 

CYL2 

C 

p 

£1 

I 

OR 

CYLl 

I 

C 

P 

E 

CYL.fi 

C 

I 

C 

P 

BCYL  VERTICAL 

180°  SHAFT 

FIG.  4. — 2-CYLiNDER  POWER  DIAGRAM,  180  SHAFT 

pression,  its  power  stroke  will  follow  the 
power  stroke  of  piston  1,  while  if  it  is  on  ex- 
haust its  power  stroke  will  have  occurred  im- 
mediately before  the  power  stroke  of  piston 


ENGINE  PRINCIPLES  25 

1.  In  either  case  one  power  stroke  follows 
the  other,  taking  place  in  one  revolution  of 
the  crank  shaft,  while  in  th0  following  revo- 
lution both  pistons  will  be  performing  dead 
strokes. 

While  there  is  no  vibration  from  the  move- 
ment of  the  pistons  in  this  engine,  the  uneven 
production  of  power  will  produce  vibration 
of  another  kind. 

These  two  types  may  be  built  with  the 
cylinders  standing  up  or  lying  down;  that 
is,  they  may  be  either  vertical  engines  or 
horizontal  engines.  The  double  opposed  en- 
gine, which  is  built  only  in  horizontal  form, 
is  free  from  either  kind  of  vibration,  but  has 
the  disadvantage  of  occupying  more  room 
than  the  others.  The  cylinders,  instead  of 
being  side  by  side,  and  on  the  same  side  of 
the  crank  shaft,  are  placed  end  to  end,  with 
the  crank  shaft  between  them,  as  shown  in 
Figure  5. 

The  pistons  make  their  inward  and  out- 


20 


TEACTOE  PEINCIPLES 


ward  strokes  together,  but  in  so  doing  they 
move  in  opposite  directions.  Thus  every 
power  stroke  is  followed  by  a  dead  stroke,  as 
in  the  engine  shown  in  Figure  3,  while  the 
movement  of  one  piston  balances  that  of  the 


R 

iT 

IV. 

2f 
REV. 

CYL  1 

I 

c 

P 

L 

CYL2 

P 

E 

I 

c  ! 

HORIZONTAL  OPPOSED  ENGINE 

FIG.  5. — H.  D.  O.  POWER  DIAGRAM 

other,  as  is  the  case  with  the  engine  shown  in 
Figure  4. 

In  a  4-cylinder  engine  one  power  stroke 
follows  another  without  any  dead  stroke  in- 
tervals, which,  of  course,  makes  the  crank 
shaft  revolve  more  smoothly  and  with  a 
steadier  application  of  power.  The  power 


ENGINE  PRINCIPLES 


27 


diagram  is  shown  in  Figure  6;  in  studying 
this  it  should  be  remembered  that  if  two  pis- 


h 

2 

3 

— 

4 

J 

i 

r 

i_ 

u 

J       U 

J 

15T 
REV 

2° 
REV 

15T 
REV 

2° 
REV 

CYL  1 

I 

C 

P 

L 

OR 

I 

C 

P 

E 

CYL  2 

C 

P 

E 

1 

E 

I 

C 

P 

CYL  3 

E 

I 

C 

P 

C 

P 

E 

I 

CYL  4 

P 

C 

r 

C 

P 

E 

I 

C 

FOUR  CYLINDER  ENGINE 

FlG.  6. — 4-CYLINDEE  POWEE  DIAGRAM 

tons  move  in  opposite  directions,  as  in  Fig- 
ure 4,  one  power  stroke  follows  another, 
while  if  they  move  in  the  same  direction,  as 


28  TRACTOR  PRINCIPLES 

in  Figure  3,  there  is  an  interval  of  one  stroke 
between  their  power  strokes. 

The  crank  shaft  of  a  4-cylinder  engine  is 
so  made  that  the  middle  pistons  move  in  the 
same  direction,  and  opposite  to  the  end  pis- 
tons. This  construction  has  been  found  to 
make  a  smoother  running  engine  than  if  pis- 
tons 1  and  3  moved  one  way  while  pistons 
2  and  4  moved  the  other. 

If  piston  1  is  on  the  power  stroke,  either 
piston  2  or  piston  3  can  follow,  for  they  are 
moving  in  the  opposite  direction.  If  we  say 
that  piston  2  is  the  next,  then  piston  4  must 
be  the  third  to  give  a  power  stroke,  for  it  is 
the  only  one  left  that  is  moving  in  the  oppo- 
site direction  to  piston  2.  Piston  3  is  thus 
the  fourth  to  move  under  power,  and  it  is 
followed  by  another  power  stroke  by  piston 
1 ;  the  firing  order  is  then  said  to  be  1,  2,  4,  3. 

If  it  is  piston  3  that  follows  piston  1,  piston 
4  will  again  be  the  third  to  produce  power, 
and  piston  2  will  be  the  fourth.  The  firing 
order  will  then  be  1,  3,  4,  2.  There  is  no 


ENGINE  PEINCIPLES  29 

other  order  in  which  a  4-cylinder  engine  can 
produce  power,  and  there  is  no  choice  between 
them. 

The  firing  order  of  an  engine  is  established 
by  the  manufacturer,  and  depends  on  the  or- 
der in  which  the  valves  are  operated. 


CHAPTER  III 

ENGINE  PAKTS 

THE  foundation  of  an  engine  is  the  base, 
which  supports  the  bearings  in  which  the 
crank  shaft  revolves,  and  to  which  the  cylin- 
ders are  attached.  The  cylinders  of  tractor 
engines  are  made  of  cast  iron,  and  the  cylin- 
der heads,  which  close  the  upper  ends  of  the 
cylinders,  are  usually  in  a  separate  piece, 
bolted  on.  The  joint  between  the  cylinders 
and  the  cylinder  head  is  made  tight  by  plac- 
ing between  them  a  gasket  of  asbestos  and 
thin  sheet  metal. 

The  crank  shaft  has  as  many  cranks,  or 
throws,  as  the  engine  has  cylinders.  Crank 
shafts  for  2-cylinder  engines  are  shown  in 
Figure  7;  the  upper  one  is  for  an  engine  of 
the  type  shown  in  Figure  3,  with  pistons  mov- 
ing in  the  same  direction.  With  both  cranks 

30 


ENGINE  PAETS 


31 


projecting  from  one  side  the  shaft  is  out  of 
balance,  so  balance  weights  are  attached  to 
the  opposite  side. 


MAIN 


FIG.   7. — 2-CYLiNDER   CBANK  SHAFT 

The  other  shaft  shown  in  Figure  7  does 
not  need  balance  weights,  for  one  crank  bal- 
ances the  other.  A  four-cylinder  crank 
shaft,  Figure  8,  is  also  in  balance. 

Crank  shafts  revolve  in  main  bearings, 


32 


TEACTOE  PEINCIPLES 


which  are  set  in  the  engine  base.    In  tractor 
engines  these  are  usually  plain  bearings,  a 


CONNECTING  RO'D  BEARINGS' 

FIG.   8. — ^-CYLINDER  CRANK  SHAIT? 

half  of  such  a  bearing  being  shown  in  Fig- 
ure 9.  This  is  a  bronze  shell  lined  with  a 
softer  metal,  making  an  exact  fit  on  the  shaft; 


Fio.  9. — HALF  or  A  PLAIN  BHAWNO 

with  the  two  halves  in  place,  the  shaft  should 
turn  freely,  but  without  looseness  or  side 


34 


TEACTOE  PEINCIPLE9 


play.    The  grooves  shown  are  to  admit  lubri- 
cating oil. 

The  piston  is  attached  to  the  crank  shaft 
by  a  connecting  rod,  which  is  illustrated  in 
Figure  10.  Pistons  are  shown  in  Figures  11 


FIG.  11. — PISTON  COMPLETE  AND  IN  SEOTION 

and  12 ;  they  are  made  as  light  as  is  consistent 
with  the  pressure  that  they  must  bear,  and 
are  hollow,  and  open  at  the  lower  end. 

The  piston  is  attached  to  the  connecting 
rod  by  a  wrist  pin,  or  piston  pin,  which  is  a 
shaft  passing  through  it  from  side  to  side, 
and  also  through  the  bearing  in  the  upper  end 


ENGINE  PAETS  35 

of  the  connecting  rod.  The  connecting  rod 
swings  on  the  wrist  pin  in  following  the  rota- 
tion of  the  crank  shaft,  and  its  attachment 
to  the  wrist  pin  must  permit  this  without  be- 
ing loose. 

The  bearings  at  the  two  ends  of  a  con- 
necting rod  are  usually  adjustable,  so  that 
wear  can  be  taken  up ;  some  of  the  methods 
of  doing  this  are  illustrated  in  Figure  10. 
In  A,  the  wrist  pin  bearing  is  a  plain  tube, 
ground  to  an  exact  fit ;  when  it  is  worn  it  must 
be  replaced.  In  B,  the  bearing  is  split,  and 
the  ends  are  drawn  together  by  a  bolt  to 
the  correct  fit.  The  bearing  in  C  is  in  two 
parts,  held  together  by  a  U-shaped  bolt,  while 
in  D  the  two  parts  are  held  together  by  a 
cap  bolted  to  the  end  of  the  connecting  rod. 
In  E,  the  end  of  the  connecting  rod  is  a 
square  loop  enclosing  the  two  parts  of  the 
bearing;  the  parts  are  held  in  the  proper  po- 
sition by  a  wedge  adjusted  by  screws. 

The  crank  shaft  bearing  of  the  connecting 
rod  shown  in  F  is  in  two  parts  which  are 


36 


TRACTOR  PRINCIPLES 


hinged  together.  G,  H,  and  K  show  the 
forms  usually  used  in  tractor  engines,  which 
consist  of  two  parts  bolted  together. 

The  wrist  pin  is  usually  firmly  attached  to 


D  L 

FIG.  12. — W*IST  PIN  FASTENINGS 

the  piston,  so  that  the  connecting  rod  swings 
on  it;  methods  of  securing  the  wrist  pin  are 
shown  in  Figure  12,  the  wrist  pin  being  held 
in  supports  cast  in  the  piston.  In  A,  the 


ENGINE  PAETS  37 

wrist  pin  is  held  by  two  set  screws,  and  in 
B,  by  pins  passing  through  it;  The  wrist 
pin  shown  in  D  is  hollow,  as  is  very  common, 
and  a  bolt  passes  through  part  of  the  piston 
and  into  the  wrist  pin. 

In  the  construction  shown  in  C  the  wrist 
pin  is  secured  to  the  connecting  rod  and 
moves  in  bearings  in  the  piston.  In  E,  a 
ring  fitting  in  a  groove  around  the  piston 
prevents  the  wrist  pin  from  moving  endways. 

The  engine  must  usually  be  taken  to  pieces 
in  order  to  get  at  the  wrist  pin;  lock  nuts, 
lock  washers  or  cotter  pins  are  always  used 
to  prevent  the  trouble  that  would  be  caused 
if  the  wrist  pin  worked  loose. 

A  leak-proof  joint  between  the  piston  and 
the  cylinder  is  made  by  means  of  piston  rings 
that  fit  in  grooves  around  the  piston,  as 
shown  in  E,  Figure  12.  Piston  ring  grooves 
are  shown  in  Figure  11.  Piston  rings  are 
not  solid,  but  are  split  so  that  they  are  elas- 
tic; they  fit  snugly  in  their  grooves,  and  tend 
to  spring  open  to  a  greater  size  than  the  cyl- 


38  TRACTOR  PRINCIPLES 

inder.  This  causes  them  to  maintain  a  close 
fit  against  the  cylinder,  and  the  gases  are 
prevented  from  leaking  past. 


CAM 


VALVE 
COMBUSTION 


FIG.  13.— VALVE 


Each  cylinder  is  provided  with  two  valves : 
the  inlet  valve  that  admits  fresh  mixture  and 
the  exhaust  valve  through  which  the  burned 


ENGINE  PARTS  39 

gases  escape.  These  valves  are  metal  disks 
with  funnel-shaped  edges  fitting  into  funnel 
holes.  A  valve  and  its  stem  are  shown  in 
Figure  13  and  also  in  Figure  15. 

A  valve  is  opened  at  the  proper  time  by  a 
cam,  and  closed  by  a  spring.  A  cam  is  a 
wheel  with  a  bulge  on  one  side,  so  that  its 


FIG.  14. — ACTION  OF  A  CAM 

rim  is  eccentric  to  its  shaft,  as  illustrated  in 
Figure  14,  which  shows  a  cam  in  three  posi- 
tions of  a  revolution.  A  rod  resting  on  the 
rim  of  the  cam  is  moved  endways  as  the  bulge 
passes  under  it,  and  the  valve  is  operated  by 
connecting  it  with  the  rod. 

A  valve  is  opened  once  during  two  revo- 
lutions of  the  crank  shaft ;  therefore  the  cam 
cannot  be  placed  on  the  crank  shaft,  for,  if 


40  TRACTOR  PRINCIPLES 

it  were,  the  valve  would  be  opened  every 
revolution.  The  cam  is  placed  on  a  separate 
shaft  which  is  driven  by  the  crank  shaft  at 
half  its  speed.  This  is  usually  done  with 
gears,  a  gear  on  the  crank  shaft  meshing  with 
a  gear  on  the  cam  shaft  having  twice  as  many 
teeth;  the  crank  shaft  gear  must  make  two 
revolutions  in  turning  the  cam  shaft  gear 
once. 

The  valve  in  Figure  13  is  held  on  its  seat 
by  a  spring.  The  cam  bears  against  the  end 
of  the  valve  stem,  and  as  it  revolves  its  bulge 
forces  the  valve  stem  and  valve  to  move  end- 
ways and  thus  to  uncover  the  valve  opening. 

As  the  movement  of  the  piston  depends  on 
the  crank  shaft,  the  valve  can  be  made  to 
open  at  the  right  time  by  a  proper  setting 
of  the  gears  that  drive  the  cam  shaft. 

The  length  of  time  that  the  cam  will  hold 
the  valve  open  depends  on  the  shape  of  the 
bulge  of  the  cam.  It  can  be  seen  that  the 
pointed  cam  of  Figure  13  will  not  hold  the 


VALVE* 


FIG.   15. — "TWIN  CITY"  TRACTOR 


41 


42  TRACTOR  PRINCIPLES 

valve  open  for  as  long  a  time  as  the  flat-end 
cam  of  Figure  14. 

In  the  design  shown  in  Figure  13  the  cam 
bears  directly  against  the  end  of  the  valve 
stem,  the  cam  shaft  in  this  case  lying  along 
the  cylinder  head.  In  the  construction  shown 
in  Figure  15  the  valves  are  not  placed  in  the 
cylinder  head,  but  are  in  an  extension  or 
v dive  pocket  projecting  from  the  combustion 
chamber;  this  cam  shaft  is  near  the  crank 
shaft.  It  would  not  be  practicable  to  make 
the  valve  stem  long  enough  to  reach  down 
to  the  cam,  so  a  length  of  rod,  called  a  push 
rod,  or  tappet,  is  placed  between  them;  the 
cam  moves  the  push  rod  and  the  push  rod  in 
turn  moves  the  valve.  This  is  a  construction 
frequently  used  for  automobile  engines. 

In  tractor  engines  the  cam  shaft  is  usually 
placed  near  the  crank  shaft,  as  in  Figure  15, 
and  the  valves  are  in  the  head,  so  that  a  valve 
moves  in  the  opposite  direction  to  the  move- 
ment of  the  push  rod.  This  requires  still  an- 
other part  to  be  used,  call  the  rocker  arm*  It 


43 


44  TRACTOR  PRINCIPLES 

is  shown  in  Figure  16.  It  is  a  short  bar, 
pivoted  at  or  near  the  center,  with  one  end 
at  the  push  rod  and  the  other  at  the  valve 
stem.  When  it  is  moved  by  the  push  rod  it 
in  turn  moves  the  valve. 

Valves  operated  by  push  rods  and  rocker 
arms  are  also  shown  in  Figures  17,  18  and 
19;  Figure  18  is  a  single-cylinder  horizontal 
engine,  while  Figure  19  is  a  horizontal 
double  opposed  engine,  in  which  one  cam 
operates  a  valve  in  each  cylinder.  Figure  20 
shows  the  valve  mechanism  of  a  vertical 
engine  in  which  all  parts,  including  the  rocker 
arm,  are  enclosed  to  protect  them  from  dust, 
and  so  they  can  run  in  oil. 

A  small  space  is  always  left  somewhere  be- 
tween the  cam  and  the  valve  stem,  to  give  the 
valve  stem  room  to  lengthen,  which  it  will 
do  when  it  gets  hot.  If  this  space  were  not 
left,  the  valve  stem,  in  lengthening  as  it  be- 
came hot,  would  strike  the  part  next  to  it, 
and  the  valve  would  be  lifted  from  its  seat. 
This  would  cause  the  engine  to  lose  power. 


46  TRACTOR  PRINCIPLES 

This  space  must  be  kept  properly  adjusted, 
and  instructions  for  this  will  be  found  in 
Chapter  XII. 

A  valve  is  held  against  its  seat  by  a  spring, 
which  must  be  compressed  when  the  valve  is 
opened.  If  this  spring  is  too  weak,  it  will 
not  hold  the  valve  tightly  on  its  seat,  while 
if  it  is  too  stiff,  the  cam  shaft  and  other  parts 
will  be  needlessly  strained  in  compressing  it. 

Friction  between  the  cam  and  the  end  of 
the  valve  stem  or  push  rod  would  cause  rapid 
wear  if  these  parts  were  not  of  hardened 
steel,  and  kept  well  oiled.  Still  further  to  re- 
duce wear,  there  is  usually  a  roller  on  the 
end  of  the  push  rod,  as  shown  in  Figure  16 
and  some  of  the  other  illustrations.  Figure 
15  shows  a  construction  in  which  the  end  of 
the  push  rod  is  a  flat  disk,  which  rotates  as 
the  cam  comes  into  contact  with  it. 

"When  the  mixture  burns,  the  top  of  the 
piston,  the  cylinder  head,  and  the  walls  of 
the  combustion  chamber  become  heated,  and 
if  it  is  not  prevented  they  will  get  so  hot  that 


47 


48  TRACTOR  PRINCIPLES 

they  will  expand  sufficiently  to  cause  the  pis- 
ton to  stick,  or  seize.  The  upper  part  of  the 
cylinder  is,  therefore,  provided  with  a  cool- 
ing system  that  keeps  these  parts  from 
getting  overheated.  Channels  are  provided 
through  which  water  is  circulated ;  the  water 
takes  the  heat  from  the  metal  parts,  becom- 
ing heated  itself,  and  then  passes  to  a  cooler, 
or  radiator,  where  it  gives  up  the  heat  to 
currents  of  air. 

In  addition  to  the  channels,  or  water  jack- 
ets, around  the  cylinder,  a  cooling  system 
includes  the  radiator,  the  connections,  and 
usually  a  pump  that  keeps  the  water  in 
motion. 

In  some  tractors,  notably  the  Fordson,  no 
pump  is  used;  the  water  circulates  because 
it  is  heated.  This  is  called  a  thermo-syphon 
system.  When  the  engine  runs,  the  water  in 
the  cylinder  jackets  becomes  heated;  as  hot 
water  is  lighter  than  cold  water,  it  rises  and 
flows  out  of  the  jackets  to  the  radiator,  its 
place  being  taken  by  cool  water  from  the  bot- 


49 


50  TRACTOR  PRINCIPLES 

torn  of  the  radiator.  This  circulation  con- 
tinues as  long  as  the  water  in  one  part  of  the 
system  is  hotter  than  the  water  in  some  other 
part  of  the  system. 

The  lubrication  of  an  engine  is  described 
and  explained  in  Chapter  X. 


FIG.  20.— "MONARCH"  ENGINE 


51 


CHAPTER  IV 

. 

FUELS  AND   CAEBUKETION 

IN  order  that  a  thing  may  burn,  it  must 
be  provided  with  oxygen.  Oxygen  is  found 
in  air,  so  it  is  usual  to  say  that  air  is  neces- 
sary in  order  that  anything  may  burn. 

To  prove  this,  light  a  candle  and  place 
an  empty  bottle  over  it,  upside  down;  in  a 
very  short  time  the  oxygen  in  the  bottle  will 
be  used  up,  and  the  flame  will  flicker  and  get 
smoky,  and  finally  die  out.  If  a  card  is  laid 
on  the  chimney  of  a  coal-oil  lamp  so  that  it 
covers  the  opening,  that  flame  also  will 
flicker,  get  smoky 'and  go  out. 

In  order  to  deaden  the  fire  in  a  stove,  the 
dampers  are  closed  to  prevent  air  from  enter- 
ing; the  fire  is  kept  alight  by  the  very  small 
quantity  of  air  that  leaks  in  below  the  fire- 
box. When  the  drafts  are  opened  the  fire  will 

52 


FUELS  AND  CAKBURETION       53 

burn  up  brightly  because  a  plentiful  volume 
of  air  can  then  enter. 

In  a  similar  way,  air  must  be  used  in  a 
gas  engine  in  order  that  the  fuel  may  burn. 
It  is  not  possible  to  mix  air  with  a  liquid; 
the  first  step  in  making  a  gas  that  will  burn 
is,  therefore,  to  turn  the  fuel,  whether  it  is 
gasoline,  kerosene,  distillate,  or  other  oil, 
into  a  vapor;  this  vapor  is  then  mixed  with 
air. 

For  good  results  it  is  very  necessary  that 
the  vapor  and  air  be  in  proper  proportions. 
In  the  experiment  with  the  candle  and  the 
bottle  it  was  seen  that  as  the  air  was  used  up, 
the  candle  flame  became  yellow  and  smoky: 
this  is  the  effect  of  insufficient  air.  If  there 
is  not  enough  air  in  the  mixture,  part  of  the 
vapor  will  not  be  able  to  burn,  and  will  only 
smoke. 

If,  on  the  other  hand,  there  is  too  much 
air,  the  mixture,  if  it  will  burn  at  all,  will 
burn  slowly,  and  the  extra  volume  of  air  will 
reduce  the  heat. 


54  TRACTOR  PRINCIPLES 

In  a  mixture  of  the  proper  proportions  of 
air  and  fuel  vapor,  the  burning,  or  combus- 
tion, will  be  very  rapid,  resulting  in  the  sud- 
den production  of  the  greatest  possible 
amount  of  heat.  This,  of  course,  is  what  is 
necessary  if  the  engine  is  to  produce  its 
fullest  power.  With  such  a  mixture,  com- 
bustion will  be  complete  before  the  piston 
has  done  more  than  start  outward  on  the 
power  stroke,  and  the  greatest  possible,  or 
maximum,  pressure  will  then  be  produced. 

When  a  mixture  burns  slowly,  the  piston 
will  have  gone  through  much  of  the  power 
stroke  before  combustion  is  complete,  in 
which  case  a  considerable  part  of  the  pres- 
sure that  should  have  been  applied  at  the 
beginning  of  the  "stroke  will  be  wasted. 

A  mixture  that  is  not  correct  will  burn 
unevenly;  it  may  burn  better  during  one 
power  stroke  than  during  another,  which  will 
make  the  engine  run  unsteadily. 

If  the  mixture  has  too  much  air  in  pro- 
portion to  the  amount  of  vapor,  it  is  known 


FUELS  AND  CAKBUKETION       55 

as  a  thin  mixture,  or  a  lean  or  poor  mixture. 
It  burns  so  slowly  that  it  is  qtiite  possible 
for  the  mixture  that  started  burning  before? 
the  beginning  of  the  power  stroke  to  con- 
tinue burning  through  the  exhaust  stroke, 
and  for  enough  flame  to  remain  in  the  cylin- 
der to  set  fire  to  the  fresh  charge  that  enters 
during  the  next  inlet  stroke.  This  will  pro- 
duce what  is  known  as  a  backfire;  that  is,  the 
mixture  entering  the  cylinder  will  catch  fire, 
and  in  burning  will  blow  back  through  the 
open  inlet  valve.  This  is  a  dangerous  condi- 
tion, for  the  flame  might  spread  to  fuel  drip- 
ping from  the  carburetor,  or  to  the  fuel  tank. 

A  mixture  that  has  not  enough  air  is  called 
a  rich  mixture;  the  air  that  is  present  will 
burn  part  of  the  vapor,  while  the  rest  will 
go  out  of  the  exhaust  unburned,  or  will  work 
past  the  piston  into  the  oil  in  the  crank  case. 
This  is  wasteful  of  fuel. 

The  most  serious  result  of  a  rich  mixture, 
however,  is  in  the  production  of  carbon,  and 
the  carbonization  of  the  engine.  The  flame  of 


56  TRACTOR  PRINCIPLES 

a  rich  mixture  is  smoky;  the  smoke  of  this 
flame,  as  is  the  case  with  smoke  from  all 
other  sources,  is  composed  of  fine  particles 
of  carbon,  or  soot.  These  particles  of  carbon 
will  deposit  on  all  parts  of  the  combustion 
space :  on  the  top  of  che  piston,  on  the  valves, 
on  the  spark  plugs,  and  on  the  inner  wall  of 
the  cylinder  head.  At  first  it  is  gummy,  but 
it  rapidly  hardens  and  forms  a  crust  that 
must  be  scraped  off  with  a  steel  tool. 

Carbon  in  an  engine  will  reduce  the  power 
through  causing  preignition,  or,  in  other 
words,  by  setting  fire  to  the  fresh  charge 
before  the  proper  point  in  the  stroke.  The 
heat  of  the  combustion  will  cause  the  carbon 
deposit  to  become  so  heated  that  it  will  glow, 
these  glowing  particles  being  sufficient  to 
ignite  the  incoming  fresh  charge.  The  rem- 
edy for  this  condition  is  to  remove  the  car- 
bon, which  is  usually  done  by  taking  off  the 
cylinder  head  and  scraping  away  the  de- 
posit. 

It  may  be  added  that  carbon  is  also  formed 


FUELS  AND  CAEBUEETION       57 

by  the  use  of  too  much  lubricating  oil,  as 
will  be  explained  in  the  chapter  on  lubri- 
cation. 

Thus  it  is  seen  that  if  the  engine  is  to 
run  properly,  and  is  to  be  kept  in  good  con- 
dition, the  proportions  of  the  mixture  must 
be  very  carefully  maintained. 

The  mixture  is  formed  in  a  carburetor,  or 
mixer.  This  is,  roughly,  in  the  form  of  a  tube 
through  which  air  is  sucked  during  the  inlet 
stroke ;  projecting  into  it  is  a  fine  tube  called 
a  spray  nozzle  through  which  the  fuel  enters. 
In  action  it  is  somewhat  similar  to  the  ato- 
mizer that  is  used  for  spraying  the  nose  and 
throat.  By  forcing  the  fuel  to  flow  rapidly 
through  this  small  tube  it  comes  out  in  the 
form  of  spray,  and  the  tiny  drops  are  picked 
up  by  the  current  of  air  and  are  carried  into 
the  cylinder. 

It  is  much  easier  to  form  a  mixture  of 
gasoline  than  of  kerosene  or  distillate,  be- 
cause gasoline  vaporizes  more  readily  at 
ordinary  temperatures.  If  saucers  of  gaso- 


58  TRACTOR  PRINCIPLES 

line  and  kerosene  are  placed  in  the  sun,  the 
gasoline  will  evaporate  rapidly  and  com- 
pletely, leaving  only  a  faint  oily  deposit.  The 
kerosene,  on  the  other  hand,  will  evaporate 
slowly,  and  much  of  it  will  not  evaporate 
at  all. 

To  make  kerosene  and  distillate  evaporate 
completely,  they  must  be  heated,  just  as 
water  must  be  heated  to  make  it  evaporate. 

In  the  case  of  a  carburetor  for  gasoline, 
the  current  of  air  needs  only  to  be  warmed; 
the  spray  of  gasoline  will  evaporate  on  com- 
ing into  contact  with  the  warmed  air,  and 
much  of  it  will  enter  the  cylinder  as  vapor. 
In  order  to  evaporate  kerosene  and  distillate 
much  more  heat  must  be  provided,  and  it  is 
usually  considered  necessary  to  heat  not  only 
the  current  of  air,  but  the  liquid  fuel  as  well. 
Methods  of  doing  this  will  be  explained  in 
the  next  chapter. 

When  kerosene  or  distillate  is  used,  there 
are  conditions  that  make  it  necessary  to  add 
water  vapor  to  the  mixture,  which  prevents 


FIG.  21. — PRINCIPLE  OP  CABBUEETOE 


60  TRACTOR  PRINCIPLES 

the  overheating  of  the  cylinder  and  reduces 
the  deposit  of  carbon.  The  difficulty  of  mak- 
ing a  complete  vapor  of  kerosene  and  dis- 
tillate results  in  a  tendency  on  the  part  of 
these  fuels  to  carbonize  the  cylinders ;  the  use 
of  water  aids  in  keeping  the  cylinders  clean. 

The  general  principle  of  a  carburetor  is 
shown  in  Figure  21,  one  drawing  illustrating 
conditions  when  the  inlet  valve  is  closed  and 
the  other  when  it  is  open.  It  shows  an  engine 
cylinder  connected  with  an  inlet  pipe  or  mix- 
ing  chamber,  through  which  there  is  a  swift 
flow  of  air  during  an  inlet  stroke. 

Projecting  into  the  intake  pipe  is  the  spray 
nozzle,  which  is  connected  with  a  small  cham- 
ber containing  fuel;  inside  of  this  chamber 
is  a  float,  usually  made  of  cork,  although  it 
is  sometimes  a  light  metal  box.  The  fuel  is 
intended  to  fill  the  chamber  to  a  certain 
height,  at  which  the  valve  will  be  closed  by 
the  float  rising  on  the  fuel.  This  level  is  such 
that  the  fuel  does  not  quite  reach  the  tip  of 
the  spray  nozzle. 


FUELS  AND  CAEBUEETION       61 

During  the  compression,  power,  and  ex- 
haust strokes,  the  fuel  stands  at  /this  level,  for 
it  cannot  run  out  of  the  spray  nozzle,  and 
the  float  holds  the  valve  closed.  As  soon  as 
the  inlet  valve  opens,  air  rushes  through  the 
intake  pipe  and  sucks  fuel  out  of  the  spray 
nozzle.  This,  of  course,  takes  fuel  out  of  the 
float  chamber;  the  float  in  sinking  opens  the 
valve,  and  enough  fuel  enters  to  restore  the 
level. 

The  fuel  comes  out  of  the  nozzle  in  the 
form  of  fine  spray ;  it  is  in  such  small  drops 
that  it  evaporates  quickly,  and  the  resulting 
mixture  of  fuel  vapor  and  air  passes  into 
the  cylinder.  By  using  a  spray  nozzle  of  the 
proper  size,  any  desired  proportion  of  fuel 
and  air  may  be  obtained. 

If  an  engine  runs  at  a  single  speed,  a  car- 
buretor as  simple  as  this  one  would  be  satis- 
factory, for  if  the  suction  is  always  the  same, 
there  will  be  little  or  no  change  in  the  pro- 
portions of  the  mixture  that  is  formed. 

To  get  the  best  results,  the  proportions  of 


62  TRACTOR  PRINCIPLES 

fuel  vapor  and  air  should  be  the  same  for  all 
running  speeds  of  the  engine.  The  propor- 
tions of  the  mixture,  however,  depend  on  the 
violence  of  the  suction,  which  changes  as  the 
engine  speed  changes,  becoming  greater  as 
the  speed  increases.  The  simple  carburetor 
illustrated  in  Figure  21  can  be  adjusted  to 
give  a  correct  mixture  for  any  particular 
speed,  but  will  be  out  of  adjustment  for  any 
other  speed. 

The  speed  of  a  1-cylinder  engine  does  not 
change  very  greatly;  it  is  built  to  run  at 
practically  a  constant  speed,  and  a  simple 
carburetor  is  satisfactory  for  it.  The  speed 
of  engines  with  a  greater  number  of  cylinders 
may  be  greatly  changed,  and  the  carburetor 
must  be  so  made  that  it  will  give  the  same 
proportions  of  vapor  and  air  at  low  speed  as 
at  high. 

In  the  simple  carburetor  described,  the 
speeding-up  of  the  engine  will  result  in  a 
greater  rush  of  air  through  the  intake  pipe, 
which  in  turn  will  suck  out  a  much  greater 


FUELS  AND  CAKBUBETION       63 

quantity  of  fuel.  If  the  carburetor  is  adjusted 
to  give  the  proper  quantity  of  fuel  for  the 
air  that  passes  at  low  speed,  at  high  speed 
it  will  give  far  more  fuel  than  will  be  re- 
quired by  the  quantity  of  air  that  then  passes. 
Thus  at  high  speed  the  mixture  will  be  too 
rich. 

If,  on  the  other  hand,  this  carburetor  is 
adjusted  to  give  a  proper  mixture  at  high 
speed,  too  little  fuel  will  be  sucked  out  when 
the  engine  runs  slowly,  and  the  mixture  will 
be  too  lean. 

A  carburetor  must  thus  have  an  additional 
device  that  will  keep  the  mixture  correct, 
regardless  of  the  speed  at  which  the  engine 
runs.  This  is  sometimes  done  by  changing 
the  size  of  the  spray  nozzle  so  that  a  greater 
or  less  quantity  of  fuel  flows  out,  but  more 
usually  by  permitting  an  extra  quantity  of 
air  to  enter  the  carburetor  as  the  engine 
speeds  up.  This  is  done  with  an  extra  air 
intake,  the  principle  of  which  is  illustrated 
in  Figure  22. 


64 


TEACTOR  PRINCIPLES 


As  will  be  seen,  this  carburetor  has  two 
openings  for  air,  one  being  the  main  air  in- 
let and  the  other  the  extra  air  inlet.  The 
latter  is  an  opening  provided  with  a  valve 
which  is  held  on  its  seat  by  a  spring.  The 


FIG.  22. — PRINCIPLE  OP  EXTRA  AIR  INLET 

suction  created  by  an  inlet  stroke  is  exerted 
in  the  carburetor,  but  at  low  speed  is  not 
sufficient  to  suck  the  extra  air  valve  from  its 
seat.  Air  then  enters  only  through  the  main 
air  inlet,  and  the  spray  nozzle  is  adjusted  to 
give  the  proper  proportion  of  fuel. 
As  the  engine  speed  increases  the  mixture 


FUELS  AND  CAKBUBETION       65 

becomes  richer;  but  there  is  also  an  increase 
in  suction,  which  becomes  strong  enough  to 
pull  the  extra  air  valve  from  its  seat.  This 
provides  another  opening  into  the  carburetor, 
through  which  enough  air  enters  to  keep  the 
mixture  in  proper  proportion.  The  higher 
the  speed  of  the  engine  the  more  the  valve 
will  open,  and  the  greater  will  be  the  quan- 
tity of  air  admitted. 

In  order  to  get  the  fullest  power  from  an 
engine,  the  carburetor  is  built  to  give  its  most 
perfect  mixture  at  the  usual  working  speed. 
This  will  be  the  speed  at  which  the  engine 
will  run  under  ordinary  conditions.  As  the 
engine  will  run  at  this  speed  most  of  the  time, 
the  carburetor  should  then  deliver  its  best 
mixture  on  the  least  possible  quantity  of  fuel. 

As  an  engine  is  run  at  low  speed  so  little 
of  the  time,  it  is  not  necessary  that  the  mix- 
ture should  then  be  so  perfect  or  that  the 
fuel  should  be  used  so  economically. 

The  design  of  a  carburetor  is  a  complicated 
matter,  because  the  production  of  mixture  is 


66  TRACTOR  PRINCIPLES 

due  to  the  flow  of  air,  which  is  a  very  change- 
able thing.  On  a  cold,  damp  day,  the  air  will 
be  heavier,  and  denser  than  on  a  day  that  is 
hot  and  dry,  and  different  quantities  of  fuel 
will  be  necessary  for  the  formation  of  the 
mixture.  The  carburetor  manufacturer  can- 
not make  a  commercial  carburetor  that  will 
take  care  of  such  a  difference  as  this;  he 
strikes  an  average  that  gives  good  general 
results,  and  expects  the  user  to  change  the 
adjustments  when  weather  and  temperature 
make  it  necessary. 

The  formation  of  the  mixture  is  affected 
by  the  condition  of  the  engine.  When  all  of 
the  parts  of  the  engine  are  tight,  the  suction 
in  the  carburetor  is  more  violent  than  when 
there  is  a  leakage  of  air  past  the  piston  rings, 
or  through  a  leaky  valve  or  spark  plug. 

On  a  dry,  hot  day  the  fuel  evaporates 
much  more  readily  than  on  a  day  that  is  cold 
and  damp;  more  of  the  fuel  that  flows  out 
of  the  spray  nozzle  will  be  vaporized  and  the 
formation  of  the  mixture  will  be  easier.  On 


FUELS  AND  CABBUEETION       67 

a  cold,  damp  day  the  fuel  will  not  vaporize 
in  the  carburetor  to  any  extent^  and  much  of 
it  will  pass  to  the  cylinder  in  drops  that  even 
there  will  not  vaporize  in  time  to  form  a  mix- 
ture. In  order  to  assure  the  vaporization  of 
enough  fuel  to  form  a  mixture  under  such 
conditions,  the  fuel  and  the  air  must  be  heated 
to  a  greater  degree. 

As  the  engine  becomes  heated  up,  more  and 
more  of  the  fuel  will  vaporize,  and  the  amount 
flowing  out  of  the  spray  nozzle  may  therefore 
be  cut  down. 

With  fuels  like  kerosene  and  distillate, 
which  do  not  vaporize  as  readily  as  gasoline, 
it  is  not  unusual  to  have  them  condense  on 
the  walls  of  the  inlet  pipe,  which  produces  a 
condition  known  as  loading.  This  condensa- 
tion is  similar  to  the  sweating  of  an  ice-water 
pitcher  on  a  hot  day.  If  an  engine  is  running 
at  a  constant  speed,  loading  does  not  make 
much  difference,  because  the  carburetor  is 
so  adjusted  that  it  gives  a  proper  mixture. 
If  the  engine  is  suddenly  speeded  up,  how- 


68  TRACTOR  PRINCIPLES 

ever,  the  greater  rush  of  air  will  pick  up 
the  condensed  fuel,  and  the  mixture  will  in- 
stantly become  too  rich,  continuing  so  until 
this  extra  supply  of  fuel  is  used  up.  The  re- 
sult will  be  to  choke  the  engine  and  make  it 
lose  power  just  at  the  time  when  extra  power 
is  needed. 

Loading  can  be  prevented  by  heating  the 
inlet  pipe  to  such  an  extent  that  the  fuel  will 
not  condense  on  it. 

The  speed  of  a  tractor  engine  is  practically 
always  controlled  by  a  throttle,  which  is  a 
valve  set  in  the  passage  of  the  carburetor. 
It  operates  exactly  the  same  as  a  damper  in 
a  stovepipe;  when  it  is  closed,  it  shuts  the 
passage  and  prevents  the  flow  of  mixture  to 
the  engine.  As  it  is  opened,  it  permits  a 
greater  quantity  of  mixture  to  flow,  and  it 
follows,  of  course,  that  as  the  charges  of 
mixture  become  larger,  the  engine  runs  with 
more  power.  A  tractor  carburetor  usually 
has  two  throttles,  one  being  operated  by  hand 
and  the  other  by  the  governor. 


FUELS  AND  CAKBUEETION       69 

It  is  usual  for  a  carburetor  to  be  fitted  with 
a  strangler,  or  choke,  which  makes  it  easier 
to  form  a  mixture  at  slow  starting  speed. 
When  an  engine  is  cold,  the  fuel  evaporates 
slowly;  and,  furthermore,  when  an  engine  is 
cranked  by  hand  its  speed  is  so  low  that  the 
suction  in  the  carburetor  is  not  sufficient  to 
draw  out  enough  fuel  to  form  a  mixture.  The 
strangler  is  a  valve  similar  in  every  way  to 
the  throttle,  but  placed  between  the  main  air 
inlet  and  the  spray  nozzle.  When  it  is  closed 
and  the  engine  is  cranked,  very  little  air  can 
enter  the  carburetor ;  the  suction  is  therefore 
very  great.  Far  more  fuel  than  usual  is  then 
sucked  out  of  the  spray  nozzle,  and  of  this 
greater  amount  enough  reaches  the  cylinder 
to  form  a  combustible  mixture.  The  engine 
will  start,  but  as  soon  as  it  does  so,  the 
strangler  must  be  opened  so  that  the  normal 
amount  of  air  enters.  If  this  is  not  done,  the 
excessive  suction  will  draw  so  much  fuel  out 
of  the  spray  nozzle  that  the  mixture  formed 
will  be  too  rich  to  burn. 


CHAPTER  V 

CARBURETORS 

THB  apparatus  that  forms  the  mixture  is 
in  two  parts,  one  being  the  carburetor  that 
proportions  the  fuel  to  the  quantity  of  air 
drawn  into  the  cylinder,  and  the  other  the 
mixing  chamber,  or  manifold,  that  connects 
the  carburetor  with  the  valve  chamber.  The 
mixing  chamber  has  no  adjustments;  it  is  a 
passage,  often  a  pipe,  that  is  shaped  to  fit  the 
conditions,  and  according  to  the  ideas  of  the 
manufacturer.  When  kerosene  and  distillate 
are  used,  the  mixing  chamber  must  be  heated, 
so  it  is  frequently  built  into  the  exhaust  mani- 
fold, which  is  the  pipe  that  conducts  the 
burned  gases  away  from  the  engine.  In  some 
cases  it  gets  heat  from  the  water  jacket  of 
the  engine,  a  water  jacket  formed  around  it 

being  connected  with  the  cooling  system. 

70 


CAEBUEETOES  71 

The  carburetor,  on  the  other  hand,  has  ad- 
justments that  must  be  understood  in  order 
to  run  the  engine  economically.  The  under- 
standing of  these  adjustments  is  simplified 
if  it  is  remembered  that  the  object  of  the 
carburetor  is  to  maintain  a  correct  propor- 
tion of  fuel  to  the  volume  of  air  that  passes 
through  it. 

All  tractor  carburetors  operate  on  the 
same  principles,  and  the  principles  are  ap- 
plied in  much  the  same  way.  If  these  prin- 
ciples are  understood,  and  there  is  an  under- 
standing of  what  the  parts  of  a  carburetor 
are  for  and  what  they  do,  there  should  be  no 
difficulty  in  adjusting  and  caring  for  any 
kind  of  a  carburetor  that  may  be  offered. 

The  main  body  of  the  carburetor  is  the  tube 
through  which  the  air  passes.  This  is  a  cast- 
ing, and  cannot  be  adjusted  or  altered.  Into 
this  passage  projects  the  spray  nozzle,  which 
is  usually  provided  with  an  adjustment  to 
control  the  amount  of  liquid  that  may  flow 
out  of  it.  When  no  adjustment  is  provided, 


72  TRACTOR  PRINCIPLES 

the  spray  nozzle  is  made  removable,  so  that 
a  nozzle  with  an  opening  of  any  desired  size 
may  be  inserted. 

On  some  carburetors  the  extra  air  valve  is 


FIG.   23. — "  KINGSTON  "   CARBURETOR,   MODEL   L 

set  by  the  manufacturers,  while  on  others  it 
is  adjustable  by  controlling  the  strength  of 
the  spring  that  holds  it  against  its  seat. 

The  carburetor  shown  in  Figure  23  has  a 
spray  nozzle  adjustment  of  a  very  usual  type. 
A  rod  is  so  arranged  that  its  pointed  end 


CAEBUEETOES  73 

projects  into  the  opening  of  the  spray  nozzle ; 
by  screwing  it  up  or  down  the  opening  may  be 
made  larger  or  smaller,  so  that  more  or  less 
fuel  may  flow  out.  The  extra  air  valve  is  a 
flap  valve  that  closes  the  air  passage  until 
the  suction  is  great  enough  to  lift  it  from  its 
seat.  Around  the  spray  nozzle  is  a  tube  that 
connects  the  passage  below  the  extra  air 
valve  with  the  passage  above  it;  when  the 
suction  is  too  low  to  lift  the  extra  air  valve 
from  its  seat,  any  air  flowing  through  the 
carburetor  passes  through  this  tube.  The 
tube  is  so  small  that  even  a  little  air  passing 
through  it  is  enough  to  suck  fuel  out  of  the 
spray  nozzle,  and  the  spray  nozzle  is  so  ad- 
justed that  enough  fuel  comes  out  to  make 
a  proper  mixture  with  that  volume  of  air. 

This  is  the  low-speed  adjustment,  which 
gives  a  mixture  on  which  the  engine  will  start 
and  will  run  at  its  lowest  or  idling  speed.  At 
this  speed  the  engine  produces  just  enough 
power  to  keep  itself  going. 

When  the  engine  speeds  up,  and  suction 


74  TEACTOB  PRINCIPLES 

increases,  the  extra  air  valve  is  lifted  off  its 
seat,  and  a  greater  volume  of  air  flows 
through  the  carburetor.  The  increased  suc- 
tion also  draws  more  fuel  out  of  the  spray 
nozzle.  If  the  greater  amount  of  fuel  were 
in  proportion  to  the  greater  volume  of  air, 
there  would  be  no  change  in  the  mixture,  but 
this  is  not  the  case.  As  suction  increases,  the 
proportion  of  fuel  drawn  out  of  the  spray 
nozzle  becomes  too  great  for  the  air,  and  the 
mixture  becomes  too  rich.  To  overcome  this, 
the  extra  air  valve  permits  a  still  greater 
volume  of  air  to  pass,  so  that  the  proportions 
of  fuel  and  air  do  not  change. 

The  chamber  below  the  air  passage  in  Fig- 
ure 22  is  the  fuel  cup,  into  which  fuel  flows 
from  the  tank.  Inside  the  fuel  cup  is  a  ring 
of  cork  attached  to  a  pivoted  lever,  on  the 
other  end  of  which  is  a  needle  valve  that  can 
close  the  opening  through  which  the  fuel 
enters  the  cup.  As  the  cup  fills,  the  cork 
floats  on  it,  and  in  rising  it  moves  the  lever 
on  its  pivot.  When  the  fuel  reaches  such  a 


CARBURETORS 


75 


level  that  it  is  near  the  tip  of  the  spray  nozzle, 
the  valve  closes  the  opening  and  prevents 
more  fuel  from  entering. 
In  the  carburetor  shown  in  Figure  24,  the 


FIG.  24. — "  KINGSTON  "  CARBURETOR,  MODEL  E 


principal  air  passage  is  past  the  spray  nozzle, 
and  all  air  goes  by  this  passage  when  the 
engine  is  running  at  low  speed.  The  extra  air 
inlet  consists  of  a  number  of  holes  through 
which  air  can  pass  without  going  past  the 


76  TRACTOR  PRINCIPLES 

spray  nozzle.  On  each  of  these  holes  is  a 
ball;  when  the  suction  is  low  the  balls  com- 
pletely close  the  holes.  When  speed  increases, 
the  suction  becomes  great  enough  to  lift  the 
balls  off  the  holes,  and  the  extra  volume  of 
air  that  is  necessary  is  permitted  to  enter. 
By  making  the  balls  of  different  weights,  it 
can  be  seen  that  the  volume  of  air  admitted 
for  any  speed  is  under  good  control. 

Like  the  carburetor  shown  in  Figure  23, 
this  carburetor  is  of  the  float  feed  type ;  that 
is,  the  flow  of  fuel  to  it  is  controlled  by  a 
valve  that  is  operated  by  a  float. 

Either  of  these  two  carburetors  may  be 
adjusted  for  gasoline  or  for  kerosene,  but 
the  adjustment  that  is  right  for  one  is  wrong 
for  the  other.  Thus,  if  an  engine  is  started 
on  gasoline,  with  the  intention  of  running  on 
kerosene,  the  carburetor  must  be  readjusted 
when  the  change  is  made.  This  is  unsatis- 
factory, so  a  double  carburetor  is  sometimes 
used,  as  shown  in  Figure  25.  This  consists 
of  two  carburetors  of  the  kind  shown  in  Fig- 


CAEBUBETOBS 


77 


ure  24,  having  a  single  mixture  outlet,  one 
being  adjusted  for  gasoline  and  tlie  other  for 
kerosene.  Either  of  them  can  be  connected 


ADJUSTMENT-^ 
MAIN 


FIG.  25. — "KINGSTON"  CARBURETOR,  DUAL  MODEL 

with  the  mixture  outlet  by  means  of  a  switch 
valve. 

In  order  to  run  on  kerosene  or  distillate 
it  is  necessary  to  apply  heat  for  the  reason 
that  these  oils  do  not  evaporate  readily  at 
ordinary  temperatures.  Gasoline,  on  the 


78  TRACTOR  PRINCIPLES 

other  hand,  evaporates  readily,  and  a  cold 
engine  can  be  started  on  it.  Tractors  that 
run  on  kerosene  or  distillate  are  therefore 
started  on  gasoline  and  run  on  it  until  they 
are  hot  enough  to  vaporize  the  heavier  oil. 

A  carburetor  that  will  run  on  either  gaso- 
line or  kerosene  is  shown  in  Figure  26.  The 
main  air  inlet  is  at  E,  which  leads  the  air 
around  the  spray  nozzle  and  into  the  cham- 
ber G.  The  mixture  flows  to  the  cylinder  by 
the  passage  B.  The  control  of  the  fuel  at 
working  speeds  is  by  the  high-speed  adjust- 
ment, which  is  a  needle  valve  screwing  into 
the  spray  nozzle.  Above  this  is  another 
needle  valve  that  adjusts  the  flow  of  fuel  for 
slow  speed. 

Extra  air  enters  through  the  opening  A, 
which  is  closed  at  slow  speed  by  a  valve  held 
against  it  by  a  spring.  This  valve  bears 
against  one  end  of  a  pivoted  lever,  the  other 
end  of  which  is  attached  to  the  slow-speed 
needle  valve ;  when  the  extra  air  valve  opens 
it  moves  the  lever  and  the  slow-speed  needle 


PIG.  26. — "E-B"  CABBUBETOB 


79 


80  TRACTOR  PRINCIPLES 

valve  is  lifted  to  permit  the  flow  of  a  greater 
volume  of  fuel  from  the  spray  nozzle. 

This  carburetor  is  started  on  gasoline. 
When  the  engine  is  hot,  a  switch  valve  is 
operated  to  permit  the  burned  gases  from  the 
engine  to  flow  through  the  carburetor;  they 
pass  through  the  pipe  C,  D,  and  as  the  cham- 
ber G  is  directly  in  their  path  it  becomes 
intensely  heated.  The  carburetor  can  then  be 
switched  to  kerosene.  A  side  view  of  this 
carburetor  is  shown  in  Figure  27. 

These  carburetors  are  all  of  the  float  feed 
type,  and  are  used  on  engines  of  which  the 
speed  is  variable.  A  carburetor  that  is  fed 
by  a  pump  is  shown  in  Figure  28.  This  is  a 
simple  tube  with  a  fuel  cup  cast  on  one  side 
of  it.  Fuel  is  pumped  to  the  bowl,  and  the 
proper  level  is  maintained  by  an  overflow 
through  which  excess  fuel  passes  back  to  the 
tank. 

This  carburetor  is  intended  for  an  engine 
of  which  the  speed  does  not  change  greatly. 
Its  only  adjustment  is  the  spray  nozzle,  and 


-UCAT  NCCOUC. 


Pro.  27.—'<E-B'J  CAEBUBETOB,  SIDE  Vow 
81 


82 


TRACTOE  PRINCIPLES 


this  is  altered  to  correspond  with,  changes  in 
engine  speed. 

If  an  engine  is  clean  and  in  good  condition, 


FIG.  28. — PUMP-FED  CARBURETOR 

it  will  run  as  well  on  kerosene  as  on  gaso- 
line, although  the  heating  effect  of  kerosene 
is  greater.  When  an  engine  is  carbonized, 
as  is  usually  the  case,  a  condition  known  aa 


CAEBUEETOES  83 

preigmtion  will  occur  unless  it  is  prevented. 
Carbon  from  unhurried  fuel  or ,  from  lubri- 
cating oil  will  deposit  on  the  piston  head  and 
the  parts  of  the  combustion  chamber,  and 
particles  will  become  heated  to  the  glowing 
point,  when  they  will  set  fire  to  the  fresh 
mixture  during  the  compression  stroke  and 
before  the  proper  time.  The  effect  is  to  make 
the  engine  lose  power,  and  it  also  gives  rise 
to  a  sharp  metallic  knocking.  By  reducing 
the  temperature  in  the  cylinder  during  the 
compression  stroke  this  condition  can  be  pre- 
vented. This  can  be  done  by  adding  water 
vapor  to  the  mixture,  and  kerosene  carbu- 
retors are  therefore  built  with  a  water  at- 
tachment. As  can  be  seen  in  Figure  28,  this 
is  a  water  cup  and  spray  nozzle  like  those 
for  the  fuel.  When  the  engine  knocks,  and 
shows  that  preignition  is  occurring,  water  is 
turned  on,  and,  being  carried  into  the  cylin- 
der, keeps  the  mixture  from  being  heated  to 
the  point  of  ignition  before  the  proper  time. 
Figure  29  shows  the  attachment  of 


S4: 


TBACTOR  PKINCIPLES 


carburetor  to  an  engine  which,  in  this  case, 
is  horizontal.  To  start  the  engine,  gasoline 
is  injected  into  the  carburetor,  as  shown ;  this 


PRIME  HERE 


PIG.  29. — "TITAN"  CARBUEBTOE 

irill  give  a  sufficiently  good  mixture  for  the 
purpose,  and  enough  heat  for  running  oa 
kerosene  is  thus  obtained. 


CHOKE 


HDCTtNG 
JACKET- 


GASOLINE 
NOZZLE 


THROTTLE 
CONTROLLED 


PIG.  30. — PUMP-FED  CARBURETOR  WITH  Two  FUEL 

85 


86  TRACTOR  PRINCIPLES 

The  carburetor  sho.wn  in  Figure  30  is  sim- 
ilar, but  has  a  bowl  and  spray  nozzle  for 
gasoline,  to  use  in  starting.  It  is  also  pro- 
vided with  a  heating  jacket  through  whick 
hot  water  or  hot  gases  may  circulate. 

In  many  cases  the  fuel  is  heated  before 
reaching  the  carburetor.  This  is  done  by 
coiling  the  feed  pipe  around  the  exhaust  pipe 
or  putting  it  in  a  jacket  through  which  hot 
water  circulates. 

Another  device  sends  the  mixture  througk 
a  chamber  heated  by  the  exhaust,  as  shown 
in  Figure  31.  Figure  32  shows  an  arrange- 
ment in  which  the  mixture  passes  through  a 
jacket  around  one  branch,  of  the  exhaust 
pipe.  By  means  of  a  switch  'valve,  A,  more 
or  less  of  the  exhaust  gases  may  be  permitted 
to  flow  through  this  branch,  so  that  the  mix- 
ture may  be  heated  to  any  desired  degree. 

All  of  these  heating  devices  are  so  arranged 
that  the  heat  is  under  the  control  of  the 
driver,  which  permits  him  to  heat  the  mix- 
ture as  much  as  he  judges  to  be  necessary. 


gv  ^^M, 


Tfw.  31.— ''HART-PAER"  MIXTURE  HEATHR 


87 


88 


TEACTOK  PRINCIPLES 


Enough  heat  must  be  used  to  prevent  the 
fuel  from  condensing;  but  too  much  heat 
will  cut  down  the  efficiency  of  the  engine  be- 


32. — "TWIN  CITY"  MANIFOLD 


cause  it  will  cause  so  much  expansion  of  the 
mixture  that  a  cylinderful  of  it  will  not  pro- 
dace  the  maximum  power. 


CARBURETORS  89 

Figure  33  shows  the  pump  that  is  used  in 
a  force-feed  carburetor  of  the  type  shown 
in  Figure  28.  Its  plunger  is  forced  through 
an  inward  stroke  by  a  cam,  and  makes  an 
outward  stroke  as  its  spring  returns  it  to 
position.  The  inlet  and  outlet  openings  of 
the  cylinder  are  closed  by  ball  check  valves, 
the  inlet  check  being  open  on  the  outward 
strokes,  and  the  outlet  check  being  open  on 
the  inward  strokes.  A  pump  of  this  sort  re- 
quires no  attention  beyond  seeing  that  the 
check  valves  work  properly,  and  that  there 
are  no  leaks. 

Figure  34  shows  the  connections  between 
the  fuel  tank  and  the  carburetor.  Under  the 
tank,  1,  is  a  chamber  containing  a  fine-wire 
strainer,  4,  through  which  the  fuel  must  pass 
to  reach  the  carburetor;  any  dirt  that  may 
be  present  is  strained  out,  and  collects  in 
the  cup,  2.  Water  in  the  fuel  also  settles 
here,  and  the  cup  is  cleaned  out  by  unscrew- 
ing the  plug,  3.  5  is  the  shut-off  cock;  it 


GASOUME  FROM  TANK3 

Fio.  33.— FUIL  PUMP 


90 


CARBURETORS  91 

should  always  be  closed  when  the  tractor  is 
not  working. 

A  complete  fuel  system  is  illustrated  in 
Figure  35,  showing  the  connections  of  the 
tanks,  pumps,  and  carburetor. 

As  dirt  is  injurious  to  an  engine,  the  air 
that  forms  the  mixture  must  be  clean,  so 
when  a  tractor  works  in  a  dusty  field,  it 
should  be  equipped  with  an  air  cleaner,  of 
which  there  are  three  kinds.  In  one  of  these 
the  air  is  required  to  pass  through  water, 
which  washes  it.  A  cleaner  of  this  type  is 
shown  in  Figure  36.  The  dusty  air  enters 
the  central  passage,  and  is  forced  to  pass 
through  the  water  in  order  to  reach  the  out- 
let Passage  through  the  water  and  through 
the  baffle  plates  frees  the  air  of  all  its  dust. 

In  the  cleaner  shown  in  Figure  37,  the  air 
is  passed  through  loose  wool,  which  filters 
out  the  dust.  Another  type  of  cleaner  works 
on  the  same  principle  as  a  cream  separator ; 
the  air  is  given  a  whirling  motion,  which 


92 


I 


I 


93 


94  TRACTOR  PRINCIPLES 

throws  the  dirt  out  at  the  sides,  and  it  is 
collected  in  a  glass  jar. 

These  air  cleaners  must  be  emptied  fre- 
quently, for  if  they  are  not  kept  clean  it  can- 
not be  expected  that  they  will  do  their  work. 

A  tractor  engine  is  built  to  develop  its 
maximum  power  at  a  certain  speed ;  if  it  runs 
at  greater  speed,  it  will  not  operate  efficiently, 
and  there  will  be  unnecessary  wear  of  its 
parts.  These  engines  are  therefore  usually 
fitted  with  governors  which  hold  them  at 
their  most  efficient  speed.  A  governor  oper- 
ates by  centrifugal  force. 

Anything  in  motion  tries  to  move  in  a 
straight  line;  if  it  is  forced  to  move  in  a 
circle,  it  will  exert  force  in  trying  to  move 
away  from  its  center.  It  is  this  that  is  called 
centrifugal  force.  It  is  centrifugal  force  that 
holds  water  in  a  pail  that  is  being  swung 
around  the  head,  and  that  makes  the  pail  fly 
off  if  it  is  released. 

In  applying  this  principle  to  a  governor, 
weights  are  attached  to  a  plate  and  made  to 


DRAIN 
PLU& 


Fio.  36. — AIR  WASHES 


96  TRACTOR  PEINCIPLES 

revolve ;  springs  hold  them  together,  but  in 
spite  of  this,  centrifugal  force  throws  them 
outward.  In  moving,  they  act  on  a  rod  that 
operates  the  throttle ;  as  the  speed  increases, 
they  move  outward  more  and  more,  and  it 


8HIPTEB 


.DiKPE* 


Fio.  37. — AIR  STRAIN** 

is  a  simple  matter  of  adjustment  to  cause 
them  to  close  the  throttle  when  the  speed 
reaches  a  desired  point. 

A  governor  and  its  connections  are  shown 
in  Figure  38.  The  weights,  R,  are  L-shaped, 
and  pivoted  at  the  angle  to  a  plate  driven 


CARBUKETOKS 


97 


by  the  engine.  The  shaft  that  drives  the 
plate  also  supports  a  collar,  P,  that  is  loose 
on  it  and  can  slide  endways ;  the  collar  rests 


FIG.  38. — "E-B"  GOVEBNOE 


against  the  short  bar  of  the  L-shaped 
weights.  The  other  end  of  the  collar  touches 
the  lever,  E,  which  is  moved  when  the  collar 


98  TEACTOB  PRINCIPLES 

moves.  As  the  lever  is  connected  with  th« 
throttle,  a  movement  of  the  collar  will  con- 
trol the  position  of  the  throttle. 

When  the  shaft  revolves,  the  long  arms  of 


FIG.  39. — "CASE"  GOVERNOR 

the  L-shaped  weights  tend  to  fly  outward; 
this  moves  them  on  their  pivots,  and  the 
short  arms  thereupon  force  the  collar  to 
slide  on  the  shaft,  which  moves  the  lever  and 
operates  the  throttle.  The  speed  at  which  the 


99 


100          TRACTOR  PRINCIPLES 

throttle  will  begin  to  close  is  determined  by 
the  setting  of  the  spring  that  holds  the 
weights  in. 

Governors  and  governor  connections  are 
shown  in  Figures  39  and  40. 

The  governor  shown  in  Figure  41  is  en- 
closed in  a  housing  that  can  be  locked  or 
sealed.  This  prevents  the  unauthorized 
changing  of  the  adjustment* 


t  41. — VERTICAL  GOVERNOB 
101 


CHAPTER  VI 

IGNITION 

IN  order  that  a  gas  engine  may  run  prop- 
erly, the  mixture  must  be  set  on  fire,  or 
ignited,  at  exactly  the  right  time;  if  ignition 
occurs  too  early  or  too  late,  there  will  be  a 
loss  of  power. 

The  greatest  pressure  will  be  obtained  at 
the  instant  when  all  of  the  mixture  is  burn- 
ing, and  this  should  take  place  just  as  the 
piston  begins  to  move  outward  on  the  power 
stroke.  A  little  time  is  required  for  the  mix- 
ture to  burn;  there  is  a  brief  interval  be- 
tween the  instant  when  it  is  set  on  fire  and 
the  instant  when  it  is  all  in  flame.  Thus  it 
is  clear  that  if  the  mixture  is  all  to  be  burn- 
ing as  the  piston  starts  the  power  stroke,  it 
must  be  set  on  fire  before  that  time,  or,  in 

102 


IGNITION  103 

other  words,  toward  the  end  of  the   com- 
pression stroke. 

The  point  at  which  ignition  should  occur 
depends  on  the  speed  of  the  engine  and 
should  change  when  the  speed  changes.  The 
time  required  for  the  flame  to  spread  through- 
out the  mixture  does  not  change;  let  us  say 
that,  with  the  engine  running  at  1200  revolu- 
tions a  minute,  the  mixture  can  be  ignited 
when  the  piston  is  14 -inch  from  the  end  of 
the  compression  stroke,  and  will  all  be  in 
flame  by  the  time  the  piston  starts  on  the 
power  stroke.  If  the  engine  is  slowed  down 
to  600  revolutions  a  minute  and  no  change 
is  made  in  the  ignition,  the  mixture  will  all 
be  in  flame  before  the  piston  reaches  the  end 
of  the  compression  stroke ;  pressure  will  then 
be  produced  before  the  piston  is  in  position 
to  perform  the  power  stroke.  The  pressure 
will  try  to  make  the  engine  run  backwards; 
it  will  sometimes  be  sufficient  to  make  the 
engine  stop.  If  the  momentum  of  the  fly- 
wheel is  sufficient  to  force  the  piston  to  the 


104          TRACTOR  PRINCIPLES 

end  of  the  stroke  against  the  pressure,  this 
condition  will  cause  a  loss  of  power.  This  is 
called  preignition,  or  ignition  that  occurs  too 
soon.  One  effect  of  it  is  to  produce  a  hard, 
metallic  knocking,  due  to  the  oil  being 
squeezed  out  of  the  bearings  by  the  great 
pressure,  which  permits  the  bearing  and  shaft 
to  strike.  The  remedy  is  to  make  ignition 
occur  later  in  the  stroke. 

If  the  engine  is  speeded  up  above  1200 
revolutions,  the  piston  will  have  had  time  to 
move  some  distance  on  the  power  stroke  be- 
fore the  mixture  is  all  in  flame ;  the  combus- 
tion space  will  then  be  too  large  to  permit 
the  mixture  to  produce  its  greatest  pressure, 
and  again  there  will  be  a  loss  of  power.  The 
remedy  in  this  case  is  to  make  ignition  occur 
earlier  in  the  compression  stroke. 

When  ignition  is  made  to  occur  early  in 
the  compression  stroke,  it  is  said  to  be 
advanced;  when  it  is  made  to  occur  late  in 
the  stroke,  it  is  said  to  be  retarded. 

To  get  the  best  results,  the  engine  should 


IGNITION  105 

be  run  with  ignition  advanced  as  far  as  is 
possible  without  causing  knocking. 

The  charge  of  mixture  is  always  set  on 
fire  by  an  electric  spark,  and  the  parts  that 
produce  and  control  this  spark  are  called  the 
ignition  system. 

An  ignition  system  consists  of:  First,  the 
apparatus  that  produces  the  electric  current, 
which  is  usually  a  magneto;  second,  a  timer, 
which  controls  the  instant  at  which  the  spark 
occurs ;  third,  the  spark  plugs,  which  project 
into  the  cylinders,  and  at  which  the  sparks 
take  place;  fourth,  a  switch,  by  which  the 
sparking  current  can  be  turned  on  or  off,  and 
fifth,  the  wires,  or  cables,  by  which  the  parts 
are  connected. 

The  electric  current  that  gives  the  spark 
is  always  produced  by  magnetism.  In  a  mag- 
neto, magnetism  is  obtained  from  the  heavy 
steel  magnets  that  are  part  of  it;  there  is  a 
constant  flow  of  magnetism  from  one  end  of 
these  to  the  other.  To  obtain  an  electric  cur- 
rent, a  coil  of  wire  is  placed  in  the  magne- 


106          TRACTOR  PRINCIPLES 

tism,  and  the  strength  of  the  magnetism  is 
made  to  change ;  it  alternately  becomes  weak 
and  strong.  "Whenever  a  change  in  strength 
takes  place,  an  electric  current  flows  in  the 
wire,  and  it  continues  to  flow  as  long  as  the 
magnetism  continues  to  change  in  strength. 
When  the  change  in  strength  is  very  great, 
that  is,  when  the  magnetism  changes  from 
very  weak  to  very  strong,  or  from  very 
strong  to  very  weak,  the  electric  current  is 
more  powerful  than  when  there  is  only  a 
little  change  in  strength.  A  more  powerful 
current  is  also  produced  by  a  change  that 
takes  place  suddenly  than  by  a  change  that 
takes  place  slowly. 

The  electrical  principle  that  produces  a 
current  in  this  manner  is  called  induction; 
the  current  produced  is  known  as  an  induced 
current. 

A  magneto  has  two  or  more  magnets,  and 
between  their  ends,  or  poles,  there  revolves 
a  piece  of  iron  called  the  armature.  A  piece 
of  iron  placed  between  the  poles  of  a  magnet 


IGNITION  107 

becomes  a  magnet  itself;  the  annatnre  is  so 
shaped  that,  as  it  revolves,  its  magnetism 
continually  changes  in  strength,  and  it  is  the 
changes  in  the  strength  of  the  magnetism  of 
the  armature  that  produce  the  sparking  cur- 
rent. 

The  iron  armature  of  the  Bosch  magneto, 


FIG.  42. — ARMATURE 

which  is  the  best  known  type,  is  shown  in 
Figure  42.  It  has  a  central  bar  with  two 
heads,  the  wire  being  wound  around  the  cen- 
tral bar,  or  core.  The  shafts  on  which  it  re- 
volves are  attached  to  the  ends  of  the  heads. 
Figure  43  shows  different  positions  of  the 
armature  between  the  poles  of  the  magnet, 
and  illustrates  the  changes  in  the  magnetism 
of  the  central  bar.  There  is  a  continual  flow 


108 


TRACTOR  PRINCIPLES 


of  magnetism  from  one  pole  of  a  magnet  to 
the  other;  if  a  piece  of  iron  lies  between  them 
the  magnetism  will  use  it  as  a  bridge,  but 
often  its  easiest  path  will  be  through  the  air. 
In  A,  Figure  43,  the  armature  lies  crossways, 
and  its  central  bar  or  core  forms  a  perfect 


A  B  C  D 

FIG.  43. — FLOW  OF  MAGNETISM  THEOUGH  ARMATURE  CORE 

bridge  for  the  magnetism.  Practically  all  of 
the  magnetism  flows  through  it,  and  it  then 
becomes  a  powerful  magnet  itself.  It  sets  up 
its  own  flow  of  magnetism,  which  flows 
through  the  core  to  one  head,  through  the 
air  to  the  other  head,  and  so  back  to  the  core. 
In  B,  the  armature  has  revolved  a  little. 
Most  of  the  magnetism  is  still  flowing  through 


IGNITION  109 

the  core,  but  some  of  it  is  finding  an  easier 
path  by  flowing  through  the  heads  and  across 
the  air  space  to  the  other  pole.  The  magne- 
tism of  the  core  is,  therefore,  a  little  weaker 
than  it  is  in  A. 

In  C,  the  heads  alone  form  bridges  between 
the  poles,  and  none  of  the  magnetism  flows 
by  the  core  because  that  no  longer  forms  a 
path.  The  core  is  no  longer  producing  mag- 
netism ;  in  moving  from  A  to  C  there  has  thus 
been  a  complete  change  in  the  strength  of 
the  magnetism  of  the  core,  for  from  full 
strength  it  has  died  away  to  nothing. 

By  a  further  movement,  as  in  D,  the  core 
again  acts  as  a  bridge,  and  another  change 
in  strength  occurs,  this  time  from  nothing 
to  full  strength  again.  In  moving  from  D  to 
B,  there  are  slight  changes  in  strength,  but 
not  enough  to  produce  a  sparking  current; 
it  is  only  in  passing  from  B  to  D  that  a  spark- 
ing current  can  be  produced. 

In  this  type  of  magneto  the  space  between 
the  heads  is  wound  full  of  wire,  which  of 


110          TRACTOR  PRINCIPLES 

course  revolves  with  the  armature ;  the  more 
turns  of  wire  there  are,  the  more  intense  will 
be  the  current,  so  very  fine  wire  is  used  to  get 
the  greatest  possible  number  of  turns. 

In  the  Bosch  magneto  the  first  few  layers 
are  of  coarse  wire,  and  are  the  primary  wind- 
ing.  The  remainder,  called  the  secondary 
minding ,  is  very  fine  wire,  and  the  two  are 
connected  so  that  one  forms  an  extension 
of  the  other. 

It  has  been  explained  that  it  is  most  im- 
portant to  have  the  spark  occur  at  exactly 
the  right  instant  in  the  stroke.  On  a  magneto 
the  instant  of  sparking  is  controlled  by  a 
timer,  or  circuit  breaker,  which  is  a  switch 
that  is  automatically  operated  at  the  time 
when  the  magneto  is  producing  a  current 
sufficiently  intense  to  form  a  spark. 

Figure  44  illustrates  one  complete  revolu- 
tion of  the  armature,  and  it  will  be  seen  that 
it  passes  twice  from  position  B  to  position  D. 
This  shows  that  it  gives  a  sparking  current 
twice  during  each  revolution.  The  circuit 


IGNITION 


111 


breaker  must  therefore  operate  twice  during 
each  revolution.  It  is  placed  at  the  end  of  the 
magneto;  in  some  makes  it  revolves  with  the 
armature  and  is  operated  by  stationary  cams, 


Fio.  44. — ONE  COMPLETE  REVOLUTION  OF  THE  ARMATURE 

while  in  others  it  is  stationary,  and  is  ope- 
rated by  a  cam  on  the  armature  shaft.  In 
either  ease  the  effect  is  the  same. 

Figure  45  shows  the  way  in  which  the  wind- 
ing on  the  armature  of  a  Bosch  magneto  is 
connected  with  the  circuit-breaker  and  with 
the  armature.  The  circuit-breaker  shown  is 


112 


IGNITION  113 

not  the  kind  used  on  the  Bosch,  and  serves 
only  to  illustrate  the  principle.  It  consists  of 
a  lever  pivoted  at  one  end,  with  the  other  end 
resting  against  the  tip  of  a  screw.  A  cam 
bears  against  the  lever  and  can  move  it  to 
break  the  contact  with  the  screw.  The  cam 
is  so  set  that  it  moves  the  lever  at  the  time 
when  the  current  is  most  intense. 

The  coarse  wire,  or  primary  winding,  on 
the  armature  is  connected  with  the  lever  and 
with  the  screw  of  the  circuit-breaker;  when 
the  lever  is  touching  the  screw,  any  current 
produced  in  the  primary  winding  has  a  com- 
plete path,  or  circuit,  in  which  to  flow. 

The  fine  wire,  or  secondary  winding,  is 
wound  on  top  of  the  primary,  and  its  inmost 
end  is  connected  to  the  outmost  end  of  the 
primary  so  that  one  forms  a  continuation  of 
the  other.  The  outmost  end  of  the  secondary 
leads  to  the  spark  plug ;  any  current  produced 
in  the  secondary  winding  flows  to  the  spark 
plug,  and,  if  intense  enough,  will  jump  across 


114         TRACTOR  PRINCIPLES 

the  small  gap  in  the  plug,  and  return  to  the 
secondary  by  way  of  the  primary. 

Referring  to  Figure  43,  a  weak  current  is 
produced  in  the  primary  while  the  arma- 
ture revolves  from  D  to  B ;  at  that  time  the 
circuit  breaker  is  closed,  so  the  current  can 
flow  in  the  path  thus  provided  for  it  A  cur- 
rent also  tries  to  flow  in  the  secondary,  but 
is  too  weak  to  jump  across  the  gap  in  the 
spark  plug.  As  the  armature  comes  closer 
to  the  point  C,  Figure  43,  the  primary  cur- 
rent becomes  more  intense,  and  the  electricity 
in  the  secondary  increases  its  endeavor  to 
jump  the  gap  in  the  spark  plug,  but  is  still 
unable  to  do  so. 

As  the  armature  passes  over  the  point  C, 
the  circuit  breaker  opens.  The  primary  cur- 
rent, which  is  then  most  intense,  finds  its  path 
taken  away  from  it,  and  it  seeks  another, 
which  it  finds  by  flowing  into  the  secondary 
winding.  This  flow  of  primary  current,  added 
to  the  pressure  already  existing  in  the  sec- 
ondary, forms  a  current  sufficiently  intense  to 


IGNITION 


115 


jump  across  the  gap  in  the  spark  plug,  and 
in  so  jumping  it  produces  the  ignition  spark. 
As  the  armature  passes  to  position  D, 
Figure  43,  the  circuit  breaker  closes,  and  the 
action  is  repeated. 


FIG.  46.— "K-W"  INDUCTOR 

A  magneto  of  this  type  is  thus  seen  to  give 
two  sparks  to  every  revolution  of  the  arma- 
ture. 

K-W  and  Dixie  magnetos  operate  on  the 
same  general  principle  as  the  Bosch,  with 
the  difference  that  the  wire  windings  are 
separate  from  the  armature,  and  do  not  re- 


116          TRACTOR  PRINCIPLES 

volve.  The  revolving  part,  which  is  called 
an  inductor,  consists  of  blocks  of  iron,  so 
shaped  that,  as  they  revolve,  they  alternately 
lead  the  magnetism  to  the  core  of  the  winding 
and  then  away  from  it.  The  result  is  that 
the  core  gains  magnetism  and  then  loses  it, 
and  these  continual  changes  in  strength  pro- 
duce sparking  currents  in  the  winding. 

The  inductor  of  a  K-W  magneto  is  shown 
in  Figure  46.  It  consists  of  a  shaft  on  which 
are  mounted  two  blocks  of  iron  at  right 
angles.  The  section  of  shaft  that  joins  them 
is  the  core  of  the  winding ;  the  wire  is  wound 
on  it  just  as  thread  is  wound  on  a  spool,  but 
with  a  space  between,  so  that  the  shaft  may 
revolve  inside  of  the  coil. 

Figure  47  shows  the  inductor  in  three  posi- 
tions of  its  revolution  between  the  poles  of 
the  magnet.  When  it  is  in  the  first  position, 
magnetism  can  flow  from  one  pole  of  the 
magnet  to  the  other  by  going  into  one  end, 
A,  of  one  block,  through  the  core,  and  out 
of  one  end,  C,  of  the  other  block.  This  makes 


IGNITION 


117 


a  magnet  of  the  core  and  it  forms  magnetism 
of  its  own.  When  the  inductor  turns  to  the 
second  position  magnetism  can  get  across 
without  flowing  through  the  core,  for  the 


FIG.. 47. — "K-W"  INDUCTOR  IN  THREE  POSITIONS 

blocks  now  give  it  a  path.  As  the  flow  through 
the  core  ceases,  the  core's  magnetism  dies 
away,  which  gives  the  change  in  strength  that 
is  needed  to  produce  a  sparking  current. 
When  the  inductor  is  in  the  third  position, 


118         TEACTOE  PEINCIPLES 
the  core  again  becomes  the  path  for  the  mag- 
netism  and   is   magnetized;    these   changes 
continue  as  long  as  the  inductor  turns. 


Fio.  48. — "Dins"  INDUCTOR 


"While  an  armature  type  of  magneto,  like 
the  Bosch,  produces  two  sparks  to  every 
revolution,  the  K-W  produces  four,  for  there 
are  four  periods  during  every  revolution 


IGNITION 

when  there  is  sufficient  change  in  the  strength?, 
of  the  magnetism  of  the  core  to  produce  a 
sparking  current. 

In  these  magnetos  the  revolving  shaft  is 
parallel  to  the  ends  of  the  magnets,  but  in 
the  Dixie  magneto  it  is  at  a  right  angle,  as 
shown  in  Figure  48.  The  shaft  is  of  some 
metal,  such  as  brass  or  bronze,  through  which 
magnetism  will  not  flow ;  otherwise  the  shaft; 
would  form  a  continuous  path.  The  inductor 
blocks  are  mounted  on  the  shaft,  and  act  as 
extensions  of  the  poles  of  the  magnet.  The 
core  on  which  the  wire  is  wound  is  a  separate 
piece,  placed  under  the  arch  of  the  magnets, 
with  ends  that  extend  down  and  form  a  tun- 
nel in  which  the  inductor  revolves. 

Figure  49  shows  an  end  view  of  the  in- 
ductor, the  magnets  being  cut  away  so  that 
the  core  may  be  seen.  As  inductor  block  A 
is  an  extension  of  one  pole  of  the  magnet, 
magnetism  tries  to  flow  from  it  to  block  B, 
which  is  an  extension  of  the  other  pole  of 
the  magnet.  When  the  inductor  is  in  position 


120 


TRACTOR  PRINCIPLES 


1,  Figure  49,  magnetism  can  flow  from  block 
A  through  the  core  to  block  B,  the  core  then 
being  magnetized.  In  position  2,  magnetism 
can  flow  from  one  block  to  the  other  by  going 
through  the  ends  of  the  core  instead  of 


1  Z  5  ' 

FIG.  49. — THREE  POSITIONS  OP  "  DIXIE  "  INDUCTOR 

through  the  core  itself;  the  core  then  loses 
its  magnetism,  but  regains  it  when  the  in- 
ductor moves  to  position  3. 

In  practically  all  makes  of  magnetos  the 
circuit  breaker  is  at  the  end  of  the  armature 
or  inductor  shaft,  and  is  operated  by  it.  The 
Bosch  circuit  breaker  is  illustrated  in  Figure 


IGNITION 


121 


50,  the  parts  being  mounted  on  a  plate  at- 
tached to  the  shaft  and  revolving  with  it. 
The  lever  is  L-shaped,  pivoted  at  the  angle, 
with  one  end  resting  on  the  tip  of  a  screw. 


ADJUSTING  NUT 
PLATINUM    POINTS 


HOUSING 

INSULATCD  BLOCK- 

FIG.  50. — "BOSCH"  CIRCUIT  BREAKER 

When  the  shaft  revolves,  the  other  end  of  the 
lever  is  dragged  over  a  block  of  metal  that 
acts  as  a  cam ;  this  makes  it  move  on  its  pivot 
and  separates  it  from  the  screw.  By  turning 
the  screw  the  distance  of  separation  may  be 
adjusted. 


122          TRACTOR  PRINCIPLES 

In  the  circuit  breaker  of  the  K-W  magneto 
it  is  the  cam  that  revolves,  while  the  lever  is 
stationary,  as  shown  in  Figure  51.  It  will  be 
noticed  that  the  cam  will  move  the  lever  only 
twice  during  each  revolution;  the  magneto 


ROLLER 

PIVOT 

FIG.  51. — "K-W"  CIRCUIT  BREAKI 


can  produce  four  sparks  during  a  revolution, 
but  with  this  arrangement  of  the  cam  only 
two  of  them  are  used. 

It  has  been  said  that  an  intense  sparking 
current  is  produced  when  there  is  a  great 
change  in  the  strength  of  the  magnetism,  and 
when  the  change  in  strength  occurs  suddenly. 


IGNITION  123 

There  cannot  be  any  alteration  in  the  change 
in  strength,  for  the  greatest  magnetic 
strength  of  the  core  is  what  is  given  it  by 
the  magnet,  and  changing  from  this  to  noth- 
ing is  the  greatest  change  possible.  The 
suddenness  with  which  the  change  takes  place, 
however,  depends  on  the  speed  at  which  the 
magneto  runs.  A  4-cylinder  engine  requires 
two  sparks  to  each  revolution  of  the  crank 
shaft ;  the  armature  of  a  Bosch  magneto  for 
this  engine  will  therefore  run  at  the  same 
speed  as  the  crank  shaft. 

The  K-W  magneto,  giving  four  sparks  to 
the  revolution,  could  run  at  half  of  the  speed 
of  the  crank  shaft,  but  then  the  change  in  the 
strength  of  the  magnetism  would  take  place 
slowly,  and  the  sparking  current  would  not 
be  sufficiently  intense.  By  using  only  two  of 
the  sparks  the  magneto  is  run  at  the  same 
speed  as  the  crank  shaft;  the  change  in 
strength  then  takes  place  more  suddenly,  and 
a  more  intense  sparking  current  is  produced. 

The  circuit  breaker  of  a  magneto  for  a 


124         TRACTOR  PRINCIPLES 

1-cylinder  engine  has  only  one  cam,  so  that 
a  single  spark  is  produced  during  each  revo- 
lution of  the  armature;  the  armature  makes 
one  revolution  to  every  two  revolutions  of 
the  crank  shaft. 

However  many  cylinders  an  engine  may 
have,  the  magneto  must  be  revolved  from  one 
point  of  sparking  to  the  next  in  the  interval 
between  ignition  in  one  cylinder  and  ignition 
in  the  next  cylinder  to  fire.  A  magneto  is 
driven  by  the  crank  shaft  through  gears  or 
by  a  chain,  which  are  so  proportioned  and 
set  that  the  magneto  is  at  a  point  of  sparking 
at  the  instant  when  a  piston  is  in  position 
for  ignition. 

A  magneto  for  an  engine  with  more  than 
one  cylinder  is  provided  with  a  distributor, 
which  passes  the  sparking  current  to  the 
particular  cylinder  that  is  ready  for  ignition. 
A  distributor  is  a  revolving  switch  built  into 
the  magneto,  with  as  many  points,  or  contacts, 
as  the  engine  has  cylinders.  At  the  instant 
when  the  magneto  produces  a  sparking  cur- 


IGNITION  125 

rent,  the  revolving  distributor  arm  is  in  posi- 
tion to  pass  the  current  to  one  of  the  con- 
tacts, and  the  current  flows  to  the  spark 
plug  with  which  it  is  connected. 

An  electric  current  must  have  a  complete 
path,  or  circuit,  in  order  to  be  able  to  flow. 
In  a  magneto  ignition  system  this  path  is 
partly  of  wire  and  partly  of  the  metal  of  the 
engine.  The  diagram  in  Figure  45  indicates 
that  the  current  returns  to  the  magneto  from 
the  circuit  breaker  lever  and  the  spark  plug 
by  wire,  but  in  actual  construction  it  returns 
by  the  metal  of  the  engine.  This  is  called  a 
groiwd  return;  the  circuit  is  said  to  be 
grounded. 

Figure  52  is  a  side  view  of  a  Bosch  mag- 
neto, partly  broken  away  to  show  the  in- 
terior. As  can  be  seen,  one  end  of  the  pri- 
mary winding  is  screwed  to  the  armature, 
and  is  thereby  connected  with  the  metal  of 
the  magneto;  as  the  magneto  is  attached  to 
the  engine  the  primary  winding  is  thus  in 
contact  with  that  also.  The  other  end  of  the 


126 


IGNITION  127 

primary  winding  leads  to  the  insulated  block 
of  the  circuit  breaker,  Figure  50.  This  block 
is  insulated  from  the  disk;  that  is,  while  it 
is  attached  to  the  disk,  it  is  kept  from  touch- 
ing it  by  means  of  pieces  of  hard  rubber  or 
mica.  Through  these  an  electric  current  can- 
not pass. 

The  lever  is  grounded ;  that  is,  it  is  in  con- 
tact with  the  metal  of  the  magneto.  When 
the  lever  touches  the  screw  of  the  insulated 
block,  current  can  flow;  when  they  are  sep- 
arated, the  circuit  is  broken. 

One  end  of  the  secondary  winding,  Figure 
52,  is  attached  to  the  outer  end  of  the  pri- 
mary. The  other  end  leads  to  the  slip  rwig, 
which  is  a  metal  rim  on  a  hard  rubber  wheel 
attached  to  the  armature  and  revolving  with 
it.  Sparking  current  flowing  to  the  slip  ring 
is  led  off  by  a  carbon  brush  and  passed  to 
the  distributor. 

Should  a  spark  plug  wire  fall  off  while  the 
engine  is  running,  the  current  would  lose  its 
path  and  would  seek  another;  it  is  quite 


128          TRACTOR  PRINCIPLES 

powerful  enough  to  make  a  path  for  itself 
by  breaking  through  the  windings.  As  this 
would  injure  the  magneto,  such  a  thing  is 
prevented  by  providing  a  safety  spark  gap, 
which  acts  like  a  safety  valve  in  giving  the 
current  a  path  when  the  regular  path  is  inter- 
rupted. It  consists  of  two  points  of  metal, 
one  attached  to  the  metal  of  the  magneto  and 
the  other  connected  with  the  slip  ring  brush ; 
it  is  a  more  difficult  path  than  the  one  through 
the  spark  plug,  but  easier  than  breaking  down 
the  windings. 

Figure  53  is  a  section  of  the  K-W  magneto. 
As  the  coil  does  not  revolve,  no  slip  ring  is 
necessary;  the  sparking  current  flows  directly 
to  the  distributor. 

To  start  an  engine,  the  crank  shaft  must 
be  turned  at  sufficient  speed  to  drive  the  mag- 
neto fast  enough  to  produce  a  spark.  With 
large  engines  this  is  often  a  difficult  matter, 
so  it  is  very  usual  to  equip  a  magneto  with 
an  impulse  starter.  One  part  of  this  is  at- 
tached to  the  magneto  shaft  and  the  other 


126 


130         TRACTOR  PRINCIPLES 

to  the  engine  shaft  that  drives  the  magneto ; 
the  two  are  connected  by  a  spring.  When 
starting,  a  catch  holds  the  armature  and  pre- 
vents it  from  turning.  The  drive  shaft  turns, 
however,  and  in  so  doing  winds  up  the  spring. 
At  a  certain  point  the  catch  is  automatically 
released,  and  the  spring  then  throws  the 
armature  over  at  a  speed  that  gives  a  good 
spark.  A  spark  is  thus  assured,  even  though 
the  engine  is  being  cranked  very  slowly. 


CHAPTER  Vtt 

BATTERY  IGNITION  SYSTEMS 

WHILS  the  greater  number  of  tractor  en- 
gines use  magneto  ignition,  many  use  bat- 
tery and  coil  systems,  which  are  the  same  in 
general  principle  as  magneto  systems,  but 
produce  magnetism  in  a  different  manner. 

Copper  is  a  nonmagnetic  metal;  that  is, 
magnetism  will  not  flow  through  it,  nor  can 
it  be  magnetized.  If  a  pile  of  iron  filings 
is  stirred  with  a  copper  wire  there  will  be  no 
effect,  as  might  be  expected ;  but  if  a  current 
of  electricity  flows  through  the  wire,  the  iron 
filings  will  cling  to  it,  as  shown  in  Figure  54, 
as  if  it  were  a  real  magnet. 

It  is  one  of  the  principles  of  electricity 
that  when  a  current  flows  through  a  wire, 
the  wire  is  surrounded  by  magnetism,  which 
continues  as  long  as  the  current  flows ;  when 

131 


132 


TRACTOR  PRINCIPLES 


the  circuit  is  broken  and  the  current  stops 
flowing,  the  magnetism  dies  away.  The  mag- 
netism produced  is  feeble  and  can  be  very 
greatly  increased  by  winding  the  wire  around 
an  iron  bar.  The  magnetism  produced  by 


FIG.  54. — MAGNETISM  IN  A  COPPER  WIRE 

the  current  then  flows  into  the  bar,  and  that, 
like  the  core  of  the  winding  of  a  magneto, 
throws  out  magnetism  of  its  own.  This  is 
indicated  in  Figure  55.  By  changing  the  in- 
tensity of  the  electric  current,  or  by  cutting 
it  off,  the  strength  of  the  magnetism  can  be 


BATTERY  IGNITION  SYSTEMS    133 

made  to  change,  and  this  change  of  strength 
can  produce  a  sparking  current. 

The  principle  employed  is  illustrated  in 
Figure  56.  A  is  a  coil  of  wire  wound  around 
one  end  of  an  iron  bar  and  connected  with 


FIG.  55. — MAGNETISM  FROM  ELECTRICITY 

a  battery;  B  is  an  entirely  separate  coil  of 
wire  wound  around  the  other  end  of  the  bar, 
with  its  ends  separated  by  a  short  distance. 
By  closing  the  battery  switch  the  current  will 
be  permitted  to  flow  in  coil  A,  and  the  bar 
will  become  magnetized ;  the  magnetism  that 


134          TRACTOR  PRINCIPLES 

it  throws  out  will  be  felt  by  coil  B.  When 
the  switch  is  opened  the  current  stops  flowing 
and  the  magnetism  dies  out  of  the  bar ;  these 
changes  in  strength  will  create  an  electric 
current  in  coil  B,  which  will  form  a  spark 


FIG.  56. — PRINCIPLE  OF  SPARK  OOIL 

as  it  passes  across  the  space  between  the 
ends. 

In  ignition  coils,  coil  B  is  wound  on  top  of 
coil  A.  Coil  A,  called  the  primary  winding, 
consists  of  a  few  layers  of  coarse  wire.  The 
more  turns  of  wire  there  are  in  coil  B,  called 
the  secondary  winding,  the  more  intense  will 
be  the  current  that  it  produces,  and  the  in- 


BATTERY  IGNITION  SYSTEMS    135 

tensity  is  also  increased  by  keeping  the  wind- 
ings close  to  the  iron  core.  The  secondary 
winding  is,  therefore,  made  of  exceedingly 
fine  wire,  and  has  a  very  great  number  of 
turns. 

To  obtain  a  spark,  a  current  is  permitted 
to  flow  through  the  primary  winding  to  cre- 
ate magnetism,  and  the  flow  is  then  stopped 
to  cause  the  magnetism  to  die  away.  The 
secondary  winding  is  affected  by  each  of 
these  changes  in  magnetic  strength.  The  bar 
loses  magnetism  more  rapidly  than  it  gains 
it,  however;  it  is  therefore  the  dying  out  of 
the  magnetism  that  has  the  greater  effect  on 
the  secondary  winding,  and  that  causes  it  to 
produce  a  sparking  current. 

To  use  this  principle  for  ignition,  the  en- 
gine is  fitted  with  a  revolving  switch,  which 
closes  the  circuit  as  a  piston  is  on  the  com- 
pression stroke,  and  then  breaks  the  circuit 
at  the  instant  when  a  spark  is  desired.  Com- 
bined with  the  revolving  switch,  or  timer,  is 
a  distributor  like  the  distributor  of  a  mag- 


136 


TEACTOE  PEINCIPLES 


neto,  which  passes  the  sparking  current  to 
the  cylinder  that  is  ready  to  receive  it. 
To  produce  an  intense  sparking  current,  it 


FIG.   57. — ' '  ATWATER-KENT  "  IGNITION  SYSTEM 

is  necessary  to  break  the  circuit  as  abruptly 
as  possible,  in  order  to  cause  the  magnetism 
to  die  away  suddenly.    Figure  57  shows  how 
this  is  done  in  the  Atwater-Kent  system. 
The  parts  of  the  circuit  breaker  are  car- 


BATTERY  IGNITION  SYSTEMS    137 

ried  on  a  plate,  in  the  center  of  which  re- 
volves a  shaft  with  a  notch  in  it.  Against  the 
side  of  this  shaft  rests  the  hooked  end  of 
the  sliding  catch;  as  the  notch  comes  under 
this  hooked  end,  the  sliding  catch  is  drawn 
forward,  only  to  be  snapped  back  by  its 
spring  as  the  notch  moves  from  under  it. 
The  lifter  is  a  bit  of  metal,  pivoted  at  one 
end,  with  its  free  end  lying  between  the  slid- 
ing catch  and  the  flat  steel  spring  that  car- 
ries one  of  the  contact  points. 

A,  Figure  57,  is  a  diagram  of  the  system. 
B  shows  the  position  of  the  parts  as  the  notch 
carries  the  sliding  catch  forward,  and  C 
shows  their  positions  as  the  spring  snaps  the 
sliding  catch  back  to  its  place.  It  will  be  seen 
that  in  thus  moving  back  it  strikes  the  lifter, 
which  in  turn  moves  the  contact  spring,  and 
so  closes  the  circuit;  but  the  circuit  is  in- 
stantly broken  as  the  parts  spring  back  to 
position.  The  movement  of  the  parts  is  so 
rapid  that  to  the  eye  they  seem  to  be  stand- 
ing still.  The  circuit  is  closed  only  for  an 


138          TRACTOR  PRINCIPLES 

instant,  but  that  is  sufficient  to  magnetize 
and  demagnetize  the  coil,  and  to  produce  a 
sparking  current. 

The  operation  of  this  system  depends  on 
the  very  great  swiftness  with  which  the  cir- 
cuit is  made  and  broken;  there  is  not  suffi- 
cient time  for  the  core  to  get  thoroughly 
magnetized,  but  such  magnetism  as  is  pro- 
duced changes  strength  so  quickly  that  it 
gives  a  sufficiently  intense  current  to  create 
an  ignition  spark. 

In  other  battery  systems  of  like  principle, 
the  circuit  is  closed  for  a  long  enough  time  to 
allow  the  core  to  become  fully  magnetized, 
the  circuit  then  being  suddenly  broken.  In 
some  of  these  systems  the  timer  breaks  the 
circuit,  while  in  others  it  is  broken  by  the 
magnetism,  through  a  vibrator. 

A  vibrator  coil  system  is  illustrated  in 
Figure  58.  The  timer  is  a  ring  made  of  some 
kind  of  insulating  material,  with  a  plate  of 
metal  set  in  it  and  forming  one  of  the  timer 
contacts.  The  other  contact  is  the  revolving 


140          TRACTOR  PRINCIPLES 

brush,  driven  by  the  engine;  the  circuit  is 
closed  when  the  brush  touches  the  metal 
plate. 

Opposite  the  end  of  the  core  is  a  flat  steel 
spring,  or  vibrator  blade,  resting  against  the 
tip  of  a  screw;  when  the  core  is  magnetized 
it  draws  the  end  of  the  blade  to  it,  and 
separates  it  from  the  screw.  The  battery 
current  flows  from  the  timer  contact  to  the 
screw,  then  to  the  vibrator  blade  and  to  the 
primary  winding  of  the  coil.  The  core  then 
becomes  magnetized,  and  draws  the  blade 
away  from  the  screw,  which  breaks  the  cir- 
cuit ;  this  causes  the  magnetism  to  die  away, 
and  a  sparking  current  is  produced  in  the 
secondary  winding  of  the  coil.  The  vibrator 
blade,  no  longer  held  down  by  the  magnetism, 
springs  back  against  the  screw;  the  circuit 
is  again  made,  and  the  action  is  repeated. 
The  movement  of  the  vibrator  blade  is  very 
rapid,  being  some  hundreds  of  vibrations  a 
second. 

A  spark  plug  is  illustrated  in  Figure  59. 


BATTERY  IGNITION  SYSTEMS    141 


CENTER  ELECTRODE- 

FIQ.  59. — SPARK  PLUG 


It  consists  of  a  metal  shell  screwed  into  the 
cylinder,  enclosing  an  insulator  of  porcelain, 
mica,  or  some  similar  material.  Through  the 
insulator  passes  the  center  electrode,  which 


142          TRACTOR  PRINCIPLES 

is  a  rod  of  metal,  with  its  lower  end  sep- 
arated by  a  short  distance  from  the  shell  or 
from  a  wire  attached  to  the  shell.  This  sep- 
aration is  the  gap  across  which  the  sparking 
current  passes,  and  at  which  the  spark  occurs. 
Spark  plugs  receive  the  pressure  of  the 
power  stroke,  and  must  be  strongly  made  in 
order  to  withstand  it.  A  leaky  spark  plug 
will  cut  down  the  power  of  the  engine,  just 
as  a  leaky  valve  will. 


CHAPTER  VIH 

TRANSMISSION 

THE  parts  of  a  tractor  by  which  the  power 
of  the  engine  is  applied  to  the  driving  wheels 
are  called  the  transmission,  and  include  the 
clutch,  the  change  speed  gear,  the  differential 
and  the  drive. 

It  has  been  shown  that  a  gas  engine  de- 
livers power  only  when  it  is  running  at  speed ; 
it  cannot  run  until  some  outside  power  drives 
it  through  the  inlet  and  compression  strokes. 

The  tractor  cannot  move  until  the  engine 
is  running  and  delivering  power,  and  it  fol- 
lows, therefore,  that  it  must  be  possible  to 
disconnect  the  engine  from  the  driving  mech- 
anism in  order  that  it  may  run  independently. 
This  is  done  by  means  of  a  clidch,  which  is 
a  device  that  connects  two  shafts,  or  dis- 
connects them. 

143 


144          TRACTOR  PRINCIPLES 

A  clutch  must  be  so  made  that  when  it  is 
engaged  it  takes  hold,  not  suddenly,  but 
gradually.  If  it  took  hold  suddenly,  the 


BRAKE:. 


FIG.  60. — INTERNAL  CLUTCH 


tractor  would  be  required  to  jump  at  once 
into  full  motion^  this  would  cause  a  severe 
straining  of  the  parts  and  probable  breakage. 


TRANSMISSION  145 

The  alternative  would  be  the  abrupt  stopping 
of  the  engine,  and  this  would  also  strain 
things. 

By  making  the  clutch  in  such  a  way  that 
it  slips,  and  takes  hold  little  by  little,  the 
tractor  starts  slowly,  and  gradually  comes 
up  to  speed ;  the  slipping  of  the  clutch  then 
ceases,  and  it  takes  hold  firmly. 

All  clutches  operate  by  the  friction  of  one 
surface  against  another;  in  some,  the  sur- 
faces are  curved  and  in  others  flat,  while 
in  still  others  the  clutch  is  a  band  around  a 
wheel,  or  drum.  A  clutch  is  operated  by  a 
hand  lever  or  by  a  foot  pedal. 

Figure  60  shows  a  type  of  clutch  that 
operates  inside  a  drum,  which  is  often  the 
overhanging  rim  of  the  flywheel.  The  shaft 
in  the  center  is  independent  of  the  flywheel, 
and  it  is  the  purpose  of  the  clutch,  which  is 
attached  to  the  shaft,  to  lock  the  shaft  and 
flywheel  together  when  the  tractor  is  to  be 
started. 

The  brake  shoes,  which  bear  against  the 


146         TRACTOR  PRINCIPLES 

drum,  form  the  ends  of  pivoted  levers,  and 
are  lined  with  an  asbestos  material  that  re- 
sists the  heat  caused  by  the  friction  against 
the  drum. 

A  cone-shaped  block  of  steel  slides  length- 
ways on  the  shaft;  when  it  is  pushed  into 
position,  it  forces  out  the  yokes,  and  thus 
presses  the  brake  shoes  against  the  drum. 

A  plate  clutch,  or  disk  clutch,  is  shown  in 
Figure  61.  The  principle  of  a  plate  clutch 
may  be  illustrated  by  placing  a  half-dollar 
between  two  quarters  and  pinching  them  with 
the  thumb  and  forefinger.  If  they  are  held 
loosely,  the  half-dollar  may  be  turned  be- 
tween the  quarters,  but  if  they  are  pinched 
tightly,  the  friction  between  the  coins  will 
be  so  great  that  one  cannot  be  turned  without 
turning  the  others. 

Attached  to  the  flywheel  are  studs,  which 
support  a  disk,  or  plate ;  this  plate  revolves 
with  the  flywheel,  and  is  practically  a  part 
of  it.  On  either  side  of  this  plate  are  other 
plates  that  are  supported  on  the  drive  shaft; 


147 


148         TRACTOR  PRINCIPLES 

they  revolve  with  it,  but  can  slide  along  it. 
The  end  of  the  shaft  is  square  and  fits  a 
square  hole  in  a  collar,  so  that  while  the  col- 
lar may  slide  along  the  shaft,  the  two  must 
turn  together.  Cams  are  mounted  on  the  hub 
of  one  of  the  plates  in  such  a  position  that 
they  can  press  the  outside  plates  together 
and  pinch  the  flywheel  plate  between.  The 
cams  are  operated  by  pressing  the  collar 
against  them. 

The  first  drawing  shows  the  clutch  out,  or 
released ;  the  flywheel  may  then  turn  without 
turning  the  shaft,  for  the  plates  are  not  in 
contact.  The  second  drawing  shows  the  clutch 
in,  or  engaged.  The  collar  is  pressed  against 
the  cams,  and  the  plates  in  turn  are  drawn  to- 
gether, pinching  the  flywheel  plate  between 
them.  The  flywheel  and  the  drive  shaft  then 
revolve  together. 

Plate  clutches  are  often  made  with  more 
than  three  plates ;  some  makes  run  in  a  bath 
of  oil,  and  some  are  intended  to  work  dry. 

In  a  cone  clutch,  the  overhanging  rim  of 


TEANSMISSION  149 

the  flywheel  is  funnel-shaped,  and  into  it  fits 
a  cone-shaped  disk  carried  on  the  end  of  the 
drive  shaft.  To  engage  the  clutch,  the  disk 
is  slid  along  the  shaft  against  the  flywheel, 
the  friction  between  the  two  being  sufficient 
to  drive  the  shaft. 

When  a  clutch  is  thrown  in  it  should  take 
hold  gradually,  slipping  at  first,  but  finally 
having  a  firm  grip.  When  it  is  thrown  out, 
it  should  release  instantly  and  completely. 

The  power  delivered  by  an  engine  depends 
on  the  bore  and  stroke  of  the  cylinder,  and 
on  the  speed.  The  greater  the  bore,  or  diam- 
eter of  the  cylinder,  and  the  greater  the 
stroke,  or  distance  the  piston  moves  in  a 
half-revolution  of  the  crank  shaft,  the  larger 
will  be  the  combustion  space,  and  the  larger 
will  be  the  charge  of  mixture  that  it  can  take 
in;  the  larger  the  charge,  the  greater  will  be 
the  power  produced  when  the  charge  burns. 

Each  cylinder  produces  power  once  during 
every  two  revolutions  of  the  crank  shaft;  if 
the  engine  runs  at  1,000  revolutions  per  min- 


150         TBACTOK  PEINCIPLES 

ute  there  will  be  twice  as  many  power 
strokes  as  there  would  be  if  it  ran  at  500 
revolutions  per  minute,  and  during  that 
minute  it  will  produce  twice  as  much  power. 

A  traction  engine  is  intended  to  run  at  a 
certain  speed,  at  which  it  will  produce  its 
greatest  power  without  overstraining  its 
parts.  This  normal  speed  for  any  particular 
engine  depends  on  the  number  of  cylinders, 
their  size  and  design,  and  other  details  estab- 
lished by  the  manufacturer.  To  get  the  best 
from  the  engine,  this  is  the  speed  at  which 
it  should  always  be  run. 

The  power  required  to  move  the  tractor 
depends  on  various  things ;  the  hardness  and 
smoothness  of  the  ground,  the  grade,  the 
load  it  is  pulling,  and  so  on.  The  tractor 
might  be  running  on  level  ground,  pulling  so 
great  a  load  that  the  engine  is  called  on  for 
all  of  the  power  that  it  can  deliver. 

On  coming  to  a  hill,  still  more  power  will 
be  required,  for  now  the  tractor  and  its  load 
must  be  lifted  as  well  as  moved  forward.  The 


TRANSMISSION  151 

engine,  already  working  at  its  limit,  cannot 
deliver  the  extra  power  needed,  and  will  slow 
down  and  stop  unless  something  is  done  to 
aid  it.  In  such  a  case,  the  change  speed  gear 
is  used  to  give  the  engine  a  greater  leverage 
on  its  work,  just  as  a  block  and  tackle  gives 
a  greater  leverage  or  purchase  to  a  man  who 
must  lift  a  heavy  weight. 

Let  us  say  that  the  normal  speed  of  the 
engine  is  1,000  revolutions  per  minute,  and 
that  it  is  so  connected  that  it  makes  40  revo- 
lutions while  the  driving  wheels  make  1,  the 
speed  of  the  tractor  being  3  miles  per  hour. 
If  it  is  a  4-cylinder  engine  there  will  thus  be 
80  power  strokes  to  every  revolution  of  the 
driving  wheels.  The  engine  is  delivering  its 
full  power  and  cannot  do  more  should  the 
tractor  be  called  on  for  an  extra  exertion, 
such  as  climbing  a  hill  or  crossing  rough 
ground. 

By  changing  the  connections  between  the 
engine  and  the  driving  wheels,  the  engine 
can  be  made  to  run  twice  as  many  revolutions 


152         TRACTOR  PRINCIPLES 

to  one  turn  of  the  driving  wheels,  which  will 
give  double  the  number  of  power  strokes; 
the  wheels  will  thus  be  turned  with  twice  the 
force.  As  no  change  is  made  in  the  speed 
of  the  engine,  the  wheels  will  now  turn  at 
half  their  former  speed,  and  the  tractor  will 
run  at  1%  miles  per  hour.  It  will,  however, 
have  twice  the  ability  to  overcome  obstacles. 

This  change  in  the  connections  between  the 
engine  and  the  drive  is  performed  by  the 
change  speed  gear,  which  is  driven  by  the 
engine  and  which  in  turn  drives  the  wheels. 

There  are  many  varieties  of  change  speed 
gears,  but  the  main  principle  in  them  all 
is  the  same,  for  they  depend  on  the  action 
of  cog-wheels,  or  gears. 

When  two  gears  running  together,  or  in 
mesh,  have  the  same  number  of  teeth,  they 
will  revolve  at  the  same  speed.  If  one  has 
half  as  many  teeth  as  the  other — 10  teeth  and 
20,  let  us  say — the  10-tooth  gear  will  make 
two  revolutions  while  the  20-tooth  gear  is 
making  one. 


TRANSMISSION  153 

There  are  two  shafts  in  a  change  speed 
gear,  one  driven  by  the  engine  and  the  other 
driving  the  wheels;  each  carries  gears  that 
mesh  with  gears  on  the  other  shaft.  These 
pairs  of  gears  are  of  different  sizes,  and  any 
pair  may  be  used;  the  shaft  driven  by  the 
engine  runs  as  the  engine  runs,  while  the 
speed  of  the  other  shaft  depends  on  the  pair 
of  gears  that  is  being  used. 

By  changing  from  one  pair  of  gears  to 
another,  the  driven  shaft,  and,  consequently, 
the  wheels,  may  be  run  at  a  greater  or  less 
number  of  revolutions,  while  the  speed  of  the 
engine  and  the  driving  shaft  do  not  change. 
The  number  of  power  strokes  that  occur  dur- 
ing one  revolution  of  the  wheels  is  thus 
changed,  and  they  turn  with  more  force  or 
with  less. 

High  speed,  or  high  gear,  means  the  com- 
bination of  gears  that  gives  the  greatest 
speed  to  the  wheels,  but  the  fewest  power 
strokes  to  each  revolution.  The  combination 
that  gives  the  slowest  speed  to  the  wheels, 


154         TRACTOR  PRINCIPLES 

but  the  greatest  number  of  power  strokes, 
is  called  low  speed,  or  low  gear. 

Many  tractors  have  but  two  speeds,  a  low 
and  a  high;  but  others  have  an  intermediate 
combination  for  conditions  too  severe  for 
running  on  high  gear  but  too  easy  for  low. 

The  change  speed  gear  mechanism  also 
provides  for  reversing  or  backing  the  trac- 
tor. Two  gears  running  together  turn  in  op- 
posite directions,  while  in  a  train  of  three 
gears  the  outside  gears  turn  in  the  same 
direction.  The  usual  combination  in  a  change 
speed  gear  uses  two  gears  for  going  ahead; 
to  run  the  driven  shaft  the  other  way,  which 
will  make  the  tractor  back,  a  third  gear  is 
meshed  between  the  two. 

The  differences  between  various  makes  of 
change  speed  gears  are  in  the  methods  used 
to  put  into  action  the  desired  pair  of  gears. 

Two  general  plans  are  used.  In  one  of 
them,  a  gear  of  each  pair  can  slide  endways 
on  its  shaft,  but  must  revolve  with  it;  thus 
it  can  be  slid  into  mesh  or  out.  In  the  other, 


SHIFT  LEVER 


Fie.  62. — PRINCIPLE  OP  SLIDING  GKAB 
155 


156         TEACTOE  PEINCIPLES 

the  gears  of  a  pair  are  always  in  mesh,  but 
one  of  them  is  loose  on  its  shaft,  so  that  shaft 
and  gear  can  revolve  independently.  To 
make  the  pair  of  gears  operate,  the  loose  gear 
is  locked  to  its  shaft. 

Figure  62  shows  the  principle  of  the  slid- 
ing gear  type.  One  part  of  the  shaft  driven 
by  the  engine  is  square,  and  fits  into  square 
holes  in  its  gears,  which  may  thus  slide  along 
it,  but  must  revolve  with  it.  Each  sliding 
gear  is  moved  by  a  shifter  block,  which  is 
operated  by  a  shift  lever.  There  is  a  shifter 
block  for  each  gear,  and  the  shift  lever  may 
be  moved  sideways  to  operate  either  one  of 
them. 

Figure  63  shows  the  jaw  clutch  type  of 
change  speed  gear,  in  which  the  gears  are  in 
mesh  all  of  the  time,  but  run  loose  on  their 
shaft  when  they  are  not  working.  The  draw- 
ing shows  bevel  gears,  which  are  used  when 
the  driving  and  driven  shafts  are  at  a  right 
angle.  The  same  principle  is  used  for  spur 


SHAFT  DRIVEN 
BY  ENGINE: 


GEAR  FOR 
FORWARD 


JAW  CLUTCH 

REVOLVING 

WITH 

ENGINE: 

SHAFT 


GEAR  AND 
JAW  CLUTCH 
LOOSE  ON    :       , 
ENGINE,  SHA.FT< 


SMAfT 

THAT 

DRIVES 

WHCCLS 


REVERSE 
FIG.  63.— PEINCIPLE  OF  JAW  CLUTCH  CHANGE  SPEED  GEAR 


157 


158         TRACTOR  PRINCIPLES 

gears  on  shafts  that  are  parallel,  as  in  Fig- 
ure 62. 

The  center  of  the  shaft  is  square,  and  fits 
a  block  that  can  slide  endways,  but  that  must 
revolve  with  it.  The  ends  of  the  block  have 
heavy  teeth  that  can  mesh  with  teeth  on  the 
hubs  of  the  loose  gears;  meshing  the  block 
with  one  of  the  gears  forces  that  gear  to 
revolve  with  the  shaft. 

The  drawing  shows  only  one  speed  for- 
ward; the  reverse  is  obtained  by  a  second 
gear  on  the  same  shaft,  which  is  placed  on 
the  opposite  side  of  the  center  of  the  driven 
gear,  and  turns  it  in  the  opposite  direction. 

When  a  tractor  turns,  the  outside  wheel 
makes  a  larger  circle  than  the  inside  wheel, 
and  has  a  longer  path  to  travel.  Both  wheels 
travel  their  paths  in  the  same  time,  so  it  fol- 
lows that  the  outside  wheel  must  move  faster 
than  the  inside  wheel,  although  both  are  being 
driven  by  the  engine.  This  is  allowed  for 
bj  the  differential,  which  is  driven  by  the 
change  speed  gear,  and  which  in  turn  drives 


TRANSMISSION  159 

the  wheels ;  it  operates  automatically  by  the 
difference  in  the  resistance  to  the  rolling  of 
the  wheels. 

The  action  of  the  differential  is  illustrated 
by  an  experiment  that  requires  a  pair  of 
wheels  on  an  axle,  like  buggy  wheels,  and  a 
stick  long  enough  to  reach  from  one  to  the 
other.  With  the  wheels  on  smooth  ground, 
put  the  ends  of  the  stick  through  the  wheels 
at  the  top,  each  end  pressing  against  a  spoke. 
Hold  the  stick  at  its  center  and  push  it  for- 
ward; the  stick  will  transmit  the  pressure  to 
the  spokes,  and  the  wheels  will  turn.  The 
wheels  being  on  smooth  ground,  there  is  equal 
resistance  to  their  movement,  and  they  will 
run  straight  forward. 

Now  repeat  the  experiment  with  the  wheels 
so  placed  that  one  is  on  a  smooth  roadway 
and  the  other  on  sand;  as  the  wheel  on  the 
smooth  surface  meets  with  less  resistance 
than  the  other  does,  it  moves  faster,  and  the 
pair  of  wheels  circles,  although  the  stick  ap- 
plies equal  pressure  to  both. 


160          TRACTOR  PRINCIPLES 

The  power  developed  by  the  engine  is 
transmitted  by  the  differential  to  both  rear 
wheels ;  when  the  wheels  meet  with  equal  re- 
sistance, they  turn  equally,  but  when  one 
wheel  meets  with  greater  resistance  than  the 
other,  it  slows  down,  while  the  other  speeds 
up  to  correspond. 

A  tractor  with  two  driving  wheels  must 
use  a  differential  in  order  to  make  turns 
easily.  Without  a  differential,  the  wheels 
would  run  always  at  equal  speed,  and  in  mak- 
ing a  turn  one  would  be  obliged  to  slip. 

The  use  of  a  differential  has  a  disadvan- 
tage, however.  If  one  wheel  is  in  a  mudhole 
and  the  other  is  on  hard  ground,  the  wheel 
in  the  mud  meets  with  little  resistance,  and 
all  of  the  power  of  the  engine  goes  to  it;  it 
spins  without  moving  the  tractor,  while  the 
other  wheel  remains  stationary.  In  such  a 
case  all  of  the  power  should  be  applied  to 
the  wheel  that  has  traction  in  order  to  move 
the  tractor,  but  this  the  differential  fails  to 
allow. 


TRANSMISSION  161 

In  some  tractors  the  differential  is  so 
made  that  the  parts  may  be  locked  together. 
This  lock  is  used  when  one  wheel  is  in  a 
mud  hole,  and  as  by  its  use  power  is  trans- 
mitted equally  to  both  wheels,  the  tractor 
moves. 

Great  care  must  be  taken  to  unlock  the 
differential  as  soon  as  the  need  for  the  lock 
has  passed,  for  otherwise  the  wheels  would 
slip  on  a  turn,  and  the  parts  of  the  trans- 
mission might  be  strained  or  broken. 

A  differential  is  usually  made  with  two 
bevel  gears  placed  face  to  face ;  between  them 
is  a  frame  holding  three  or  more  small  bevel 
gears  that  are  in  mesh  with  them  both.  The 
engine  revolves  the  frame  with  its  small 
gears ;  each  of  the  large  bevel  gears  revolves 
a  driving  wheel. 

When  the  tractor  moves  straight  ahead  the 
differential  turns  as  if  it  were  one  solid 
piece.  When  there  is  less  resistance  to  one 
driving  wheel  than  to  the  other,  the  small 
bevel  gears,  in  addition  to  revolving  with 


162         TEACTOE  PEINCIPLES 

the  frame  that  carries  them,  turn  on  their 
shafts.  This  transmits  the  power  of  the 
engine  to  one  wheel  more  than  the  other, 
according  to  the  resistance  of  the  wheels. 

Figure  64  shows  one  of  the  large  bevel 
gears  of  a  differential,  with  the  three  small 


yje.  (j4. — "i.  H.  C.M  CHAIN  DRIVE,  SHOWING  TSI.  DIF- 
FERENTIAL 

gears,  the  other  large  bevel  gear  being  re- 
moved. A  differential  in  section  is  shown  in 
Figure  65. 

A  tractor  with  only  one  driving  wheel  has 
no  differential.  Such  tractors  usually  have 
two  wheels,  but  one  of  them  runs  loose  on  the 
axle,  and  serves  only  to  support  the  tractor. 


TRANSMISSION  163 

The  rear  axle  construction  of  a  tractor  with 
a  1-wheel  drive  is  shown  in  Figure  66,  which 
should  be  compared  with  the  2-wheel  rear 
construction  shown  in  Figure  65. 


FIG.  65. — "CASE"  REAR  AXLE 

There  are  a  number  of  methods  used  for 
transmitting  power  to  the  driving  wheels. 
In  Figure  64  a  chain  is  used ;.  there  are  trac- 
tors with  but  one  chain,  and  others  with  a 
chain  for  each  driving  wheel. 


164 


TRANSMISSION  165 

The  most  usual  method  is  by  a  master  gear, 
or  bull  gear,  which  is  a  large  and  heavy  gear 
attached  to  the  driving  wheel,  as  shown  in 
Figures  65  and  66.  In  some  tractors  this 
gear  is  nearly  the  size  of  the  wheel,  and  is 


FIG.  67. — DRIVING  WORM 

fully  exposed;  in  others  it  is  smaller,  and 
enclosed  in  an  oil-tight  housing. 

The  small  gears  that  drive  the  bull  gears 
are  on  the  ends  of  the  cross  shaft,  called  the 
jack  shaft,  that  carries  the  differential. 

In  the  Fordson  tractor  the  differential  is 


166         TRACTOR  PRINCIPLES 

built  into  the  axle,  as  it  is  in  an  automobile, 
and  power  is  applied  by  a  worm.  The  worm 
is  driven  by  the  change  speed  gear,  and  is  a 
screw  meshing  with  a  gear  on  the  differential, 
whose  teeth  are  cut  at  the  proper  angle  to 
make  them  fit  the  threads  of  the  worm.  A 
worm,  which  is  shown  in  Figure  67,  is  al- 
ways enclosed,  and  runs  in  oil. 


CHAPTEE  IX 

TRACTOR    ARRANGEMENT 

THE  uneven  ground  over  which  tractors 
must  work  requires  the  weight  to  be  kept  low, 
to  prevent  capsizing,  and  they  are  also  built 
wide,  for  the  narrower  they  are  the  more 
easily  they  tip  over.  They  cannot  be  broad 
in  front,  however,  for  if  they  are  the  steer- 
ing wheels  cannot  be  swung  enough  to  per- 
mit them  to  turn  in  the  small  circle  that  is 
desirable. 

To  give  a  small  turning  circle  some  trac- 
tors are  built  with  the  front  of  the  frame 
raised  enough  to  permit  the  wheels  to  cut 
under.  Others  use  small  steering  wheels,  but 
this  is  not  desirable  because  small  wheels 
will  not  run  over  rough  ground  as  readily  as 
large  ones,  and  steering  is  difficult. 

Types  of  tractors  are  indicated  in  Figures 

167 


o 

a 
o 
o 
o 


A 


o 


O 

o 
o 
o 


D 


FIG.  68. — TRACTOR  ARRANGEMENT 
168 


ih 


o 
o 
o 
o 


ih 


* 


n 


C3 


F 


0 


_J  Q          L_J 


FIG.  69. — TRACTOR  ARRANGEMENT 


170         TRACTOR  PRINCIPLES 

68  and  69.  A  has  a  4-cylinder  vertical  engine 
in  front,  driving  both  wheels  by  bull  gears, 
while  B  is  a  2-cylinder  horizontal  engine  in 
the  center,  driving  both  wheels  by  chains. 
C  has  a  4-cylinder  vertical  engine  set  across 
the  frame.  These  three  types  have  riveted 
steel  frames,  to  which  the  parts  are  attached. 

In  D,  the  drive  is  entirely  enclosed  within 
the  rear  axle  housing,  and  the  rear  part  of 
the  frame  is  formed  by  the  axle  housing  and 
the  housing  of  the  change  speed  gear. 

E  has  a  1-cylinder  horizontal  engine  with 
a  single  chain  drive,  while  F  has  a  similar 
engine  but  drives  to  both  wheels. 

G  has  no  frame,  its  place  being  taken  by 
the  crank  case  of  the  engine  and  the  housings 
of  the  parts  of  the  transmission.  G  and  H 
have  4-cylinder  vertical  engines,  G  driving 
through  an  enclosed  rear  axle  and  H  through 
bull  gears. 

Figure  70  has  one  broad  wheel  instead  of 
two  narrower  ones,  this  being  placed  inside 
of  the  frame  instead  of  outside.  It  has  a  4- 


171 


172 


TRACTOR  PRINCIPLES 


cylinder  vertical  engine  placed  across  the 
frame,  and  drives  through  two  chains. 


The  front  axle  of  a  tractor  is  almost  always 
attached  to  the  frame  by  a  pivot,  so  that  the 


TRACTOR  ARRANGEMENT      173 

wheels  will  follow  uneven  ground.  Some  of 
the  forms  of  front  axles  are  shown  in 
Figure  71. 

The  first  is  a  plain  bar,  while  the  second 
is  arched  to  raise  the  front  of  the  frame  in 


5PRING 


AXLE: 

'BEARING 


FIG.  72. — SPRING  SUPPORT 

order  to  permit  the  steering  wheels  to  cut 
under.  In  the  third  the  wheel  axles  are 
mounted  on  springs,  which  take  up  some  of 
the  vibration  and  act  as  shock  absorbers. 

The  fourth  axle  shown  is  built  of  steel  bars 
riveted  together  to  form  a  truss,  and  the 


174         TRACTOR  PRINCIPLES 

fifth  is  similar,  with  the  frame  pivot  carried 
on  springs.  The  sketches  at  the  bottom  indi- 
cate the  extent  to  which  the  pivoted  front 
axle  may  swing. 

Figure  72  shows  a  spring  support  for  the 
axles,  front  and  rear.  The  axle  bearing  is  in 
a  block  sliding  in  guides,  the  weight  being 
supported  by  a  heavy  spring. 


CHAPTER  X 

LUBRICATION 

THE  most  important  thing  in  the  care  of  a 
tractor  is  to  oil  it ;  every  moving  part  should 
be  lubricated,  and  the  greatest  care  should 
be  taken  to  assure  a  never-failing  supply  of 
oil  and  grease. 

Carelessness  in  lubrication  is  the  principal 
cause  of  tractor  trouble.  There  is  nothing 
complicated  or  difficult  about  keeping  a  trac- 
tor properly  oiled;  yet  more  tractors  break 
down  from  careless  lubrication  than  from 
any  other  cause.  Every  tractor-maker  issues 
an  oiling  diagram  and  oiling  instructions, 
and  there  is  no  excuse  for  an  operator  whose 
machine  does  not  get  the  right  kind  of  lubri- 
cant in  the  right  quantity  at  each  place  where 
lubrication  is  necessary. 

The  eauee  of  wear  is  friction;  oil  reduces 
175 


176          TRACTOR  PRINCIPLES 

friction  and  so  reduces  wear.  No  matter 
how  smooth  and  highly  polished  two  pieces 
of  steel  may  be,  there  will  be  friction  between 
them  if  they  are  rubbed  together,  and  they 
will  wear  each  other.  If  they  are  oiled,  the 
particles  of  oil  will  keep  the  pieces  from 
touching  each  other,  and  there  will  be  no 
wear. 

Other  substances  than  oil  can  be  used; 
there  are  some  kinds  of  machinery  that  are 
lubricated  with  water,  for  instance.  For  gen- 
eral use,  however,  oil  and  grease  are  the  best, 
and  are  practically  always  used. 

The  object  of  a  lubricant  is  to  keep  two 
pieces  of  metal  from  touching;  it  must  there- 
fore be  able  to  get  between  them,  and  must 
stay  there.  If  the  pieces  are  large  and 
heavy,  there  will  be  much  greater  pressure 
on  the  oil  than  if  they  are  small  and  light,  and 
the  oil  must  be  able  to  withstand  this  pres- 
sure and  resist  being  squeezed  out.  The  oil 
that  would  keep  the  small,  light  pieces  apart 
might  not  be  able  to  stand  the  pressure  of 


LUBRICATION  177 

a  greater  weight,  and  might  be  squeezed  out 
from  between  two  heavy  pieces. 

Oil  has  a  tendency  to  cling  to  whatever 
it  touches,  and  thick  oil  or  grease  has  more 
of  this  tendency  than  a  thin,  or  "  runny "  oil. 
If  a  thick  oil  or  grease  is  used  on  light  ma- 
chinery, such  as  a  sewing  machine,  this  cling- 
ing tendency  would  make  the  machine  run 
hard,  and  might  even  prevent  its  operation. 

When  oil  is  heated,  it  becomes  thinner,  or 
more  " runny."  Through  this,  an  oil  used 
in  a  hot  place  might  get  so  thin  that  it  would 
not  lubricate;  and  on  the  other  hand,  an  oil 
that  works  all  right  in  the  heat  of  summer 
might  get  so  thick  on  a  cold  winter  day  as  to 
be  useless. 

A  slow-moving  part  of  a  machine  uses  a 
thick  oil  or  a  grease ;  a  thin  oil  must  be  used 
for  a  part  that  moves  at  high  speed. 

Some  of  the  parts  of  a  tractor  move  slowly 
and  some  at  high  speed;  some  are  cool  and 
some  are  hot.  Different  kinds  of  lubricants 
are  therefore  required,  and  it  is  a  grave  mis- 


178          TRACTOR  PRINCIPLES 

take  to  use  a  lubricant  that  is  not  suitable  to 
the  work  that  it  is  required  to  do. 

The  engine  is  the  most  difficult  part  of  a 
tractor  to  lubricate,  and  the  part  that  suffers 
most  if  the  supply  fails  or  if  the  wrong  kind 
of  lubricant  is  used.  In  the  first  place,  it  is 
so  hot  that  any  oil  will  burn,  being  turned 
to  carbon;  the  best  that  can  be  expected  of 
an  oil  is  that  it  will  resist  burning  until  it 
has  done  its  work  of  lubricating  the  piston 
and  cylinder. 

A  tractor  engine  is  more  difficult  to  oil 
than  an  automobile  or  truck  engine  for  the 
reason  that  it  works  harder  and  more  stead- 
ily. An  automobile  engine  is  rarely  driven 
to  the  limit  of  its  power ;  it  has  frequent  op- 
portunities to  cool  when  running  down  hill. 
A  tractor  engine,  on  the  other  hand,  works 
at  its  full  power  all  day  long  with  no  oppor- 
tunities to  cool  off.  An  oil  that  gives  good 
satisfaction  on  an  automobile  might  ruin  a 
tractor  engine  through  its  inability  to  with- 
stand the  greater  heat. 


LUBRICATION  179 

The  makers  of  tractors  understand  the  im- 
portance of  using  proper  oils,  and  recom- 
mend certain  brands  and  grades ;  these  rec- 
ommendations should  be  followed  in  order 
to  get  the  best  possible  results.  All  makers 
specify  at  least  two  kinds  of  lubricants,  and 
most  of  them  three;  one  specifies  six,  which 
range  from  a  light  sewing  machine  oil  to  a 
grease  so  thick  that  it  is  nearly  solid.  What- 
ever the  recommendations  may  be,  they 
should  be  followed. 

In  general,  lubricants  are  classified  accord- 
ing to  their  thickness,  and  they  range  from 
the  light  oil  used  for  typewriters  and  sew- 
ing machines  to  grease  so  thick  that  it  may 
be  cut  like  butter.  The  thinnest  oil  is  used 
for  the  circuit  breaker  pivot;  this  part  is 
usually  moved  in  one  direction  by  a  cam  and 
in  the  other  by  a  light  spring.  A  thick  oil 
would  gum  the  bearing  to  such  an  extent  that 
the  spring  might  not  be  able  to  move  the 
lever. 
*  The  oil  used  in  an  engine  is  thicker,  and 


KEY 

DESCRIPTION 

QUANTITY 

LUBRICATION' 

ONCE  EVERY  HOUR 


L 

Rear  axle  bearing 

Two  complete  turns 

Cup  Grease 

ONCE  EVERY  TWO  HOURS 


A 
B 

Differential  hub 
Rear  wheel  hub 

One  complete  turn 
One  complete  turn 

Cup  Grease 
Cup  Grease 

C 
H 
T 

Differential  pinion 
Front  wheel  hub 
Governor  and  cam- 

One complete  turn 
Two  complete  turns 
Two  complete  turns 

Cup  Grease 
Cup  Grease 
Cup  Grease 

shaft  bearing 

TWICE  EVERY  DAY 


E 

Governor 

Oil 

Cylinder  oil  g} 

F 

Outboard  bearing 

Two  complete  turns 

Cup  Grease 

G 

grease  cups 
Transmission 

when  plowing 
One  pint 

See  note  below 

N 

(  Magneto  trip 
<  Magneto    roller    and 
I   slide 

Grease  every  5  hours 
Oil  every  5  hours 

Cup  Grease 
Oil 

J 
W 

Steering  worm 
Steering   hub   grease 

Keep  covered 
One  complete  turn 

Cup  Grease 
Cup  Grease 

V 

cups 
Steering  worm  shaft 

Oil  every  5  hours 

R 

Lubricator  eccentric 

Oil  every  5  hours  (keep 

wool  in  pocket) 

P 

Cam  roller  slide 

Oil  every  5  hours 

K 

Valve  levera 

Fill  with  oil  every  5  hours 

(keep  wool  in  pockets) 

ONCE  EVERY  DAY  TRACTOR  IS  IN  USE 


u 

Steering  sector  shaft 

One  complete  turn 

Cup  Grease 

MECHANICAL  LUBRICATOR 

Fill  with  a  good  grade  of  heavy  gas  engine  cylinder  oil.  Turn  the 
crank  on  the  mechanical  oiler  40  to  50  times  when  starting  the 
engine. 

IMPORTANT 

In  cool  or  cold  weather  the  oil  in  lubricator  tank  must  be  warmed 
as  it  will  not  flow  readily  unless  of  the  right  temperature. 


TRANSMISSION 

In  warm  weather,  use  heavy  oil  such  as  "600"  transmission  or 
Polarine  transmission  oil ;  in  cold  weather,  use  a  good  light  oil. 

GOVERNOR 

Cylinder  oil  in  governor  should  cover  shoe. 

MAGNETO 

Oil  magneto  bearings  once  a  week  with  sewing  machine  or  cream 
separator  oil. 

181 


182          TRACTOR  PRINCIPLES 

has  a  high  burning  point  and  high  viscosity; 
that  is,  it  should  be  able  to  resist  burning, 
and  should  not  get  so  thin  when  it  is  heated 
that  it  will  be  squeezed  out  of  the  bearings. 
The  same  kind  of  oil  that  is  used  in  the  en- 
gine can  be  used  in  many  other  parts  of  the 
tractor. 

Grease  is  usually  used  for  the  gears  of  the 
transmission  and  drive.  There  is  very  great 
pressure  between  the  teeth  of  two  meshing 
gears,  and  only  thick  oil  and  grease  have  suf- 
ficient viscosity  to  resist  being  squeezed  out. 

The  thickest  grease  is  used  on  the  tracks 
of  caterpillar-type  tractors. 

Before  operating  a  tractor,  the  lubrication 
chart  supplied  by  the  manufacturer  should 
be  studied  with  great  care,  and  all  of  its  re- 
quirements should  be  observed.  This  chart 
is  usually  in  the  form  of  a  diagram  accom- 
panied by  a  table,  as  shown  in  Figure  73, 
which  is  the  lubrication  chart  of  one  of  the 
International  Harvester  tractors.  This  fig- 
ure illustrates  the  constant  attention  that  is 


184          TRACTOR  PRINCIPLES 

demanded  by  this  most  important  part  of 
tractor  operation. 

The  table  calls  for  four  lubricants,  these 
being  sewing  machine  oil,  which  is  very  thin 
and  liquid ;  gas  engine  cylinder  oil ;  transmis- 
sion oil,  which  is  as  thick  as  molasses;  and 
cup  grease,  which  is  like  butter. 

The  engine  is  oiled  automatically,  the  only 
requirements  being  to  keep  the  oil  tank  filled, 
and  to  be  sure  that  the  oiler  is  working.  The 
other  parts  of  the  tractor  are  oiled  or  greased 
by  hand. 

Figure  74  is  the  oiling  chart  of  the  Illinois 
tractor. 

There  are  three  systems  used  for  engine 
lubrication :  splash,  force  feed,  and  by  a  me- 
chanical oiler.  In  the  splash  system,  a  pool 
of  oil  is  maintained  in  the  crank  case,  of  such 
a  depth  that  the  ends  of  the  connecting  rods 
just  dip  into  it.  They  strike  it  with  sufficient 
force  to  splash  it  to  all  parts  of  the  crank 
case,  the  oil  that  strikes  the  pistons  being 


LUBRICATION 


185 


carried  up  into  the  cylinders  and  lubricating 
the  walls. 

The  end  of  the  connecting  rod  is  often 
fitted  with  a  dipper,  as  shown  in  Figure  75, 
to  strike  into  the  oil,  as  well  as  an  oil  catcher, 
shown  in  the  same  drawing,  which  is  a  little 


FIG.  75. — END  OF  "TWIN  CITY"  CONNECTING  BOD 

trough  that   catches   the   splashing  oil  and 
guides  it  to  the  connecting  rod  bearing. 

To  oil  the  wrist  pin  bearing  there  is  an 
oil  groove  around  the  piston  that  collects  oil 
from  the  cylinder  walls ;  a  hole  connects  this 
groove  with  the  hollow  wrist  pin,  from  which 
other  oil  holes  lead  to  the  bearing.  This  is 
shown  in  Figure  76. 


186 


TEACTOE  PEINCIPLES 


In  the  force  feed  system  a  pump  driven  by 
the  engine  forces  oil  through  pipes  and  chan- 
nels to  all  of  the  bearing  surfaces.  Oil  col- 
lects in  a  pocket  in  the  crank  case,  called  the 


FIG.  76. — WRIST  PIN  LUBRICATION 

sump,  and  is  drawn  from  it  by  the  pump. 
The  sump  is  usually  provided  with  a  wire 
mesh  strainer  that  separates  out  any  dirt. 

From  the  oil  pump  the  oil  is  forced  to  the 
bearings  by  pipes  and  by  holes  drilled  in  the 


187 


188          TRACTOR  PRINCIPLES 

crank  shaft  and  other  parts,  as  shown  in  Fig- 
ure 77. 

An  oil  pump  is  illustrated  in  Figure  78. 
It  consists  of  a  plunger  driven  by  the  engine, 


TO  ELWGINC. 

FIG.   78. — OIL  PUMP 


working  in  a  cylinder  provided  with  two  ball 
check  valves,  one  for  inlet  and  the  other  for 
outlet.  On  an  upward  stroke  of  the  plunger 
the  cylinder  fills  with  oil,  which  is  forced  to 


LUBRICATION  189 

the  engine  bearings  by  the  following  inward 
stroke. 
Figure  79  shows  a  similar  pump  with  a 


FIG.  79.— "E.  B."  OIL  PUMP 

strainer  over  the  intake,  the  outlet  being 
through  the  holes  L  in  the  pipe  H.  In  the 
pump  illustrated  in  Figure  80  the  plunger  is 
hollow,  and  fills  with  oil  during  an  inward 


190 


TRACTOR  PRINCIPLES 


stroke;  the  oil  is  forced  out  to  a  passage 
around  the  plunger,  and  passes  to  the  bear- 
ings by  the  holes  H. 


7  E  MOVE  PLUG  HERE 
TO  DRAIN  01 L 

FIG.  80. — OIL  PUMP  WITH  HOLLOW  PLUNGER 


Figure  81  shows  two  methods  of  prevent- 
ing oil  from  leaking  out  around  the  plunger. 
In  the  first  of  these,  a  channel  is  formed  in 
the  upper  part  of  the  pump  cylinder,  leading 


LUBRICATION 


191 


to  the  crank  case ;  any  oil  that  leaks  past  the 
plunger  flows  to  the  crank  case  by  this  drain 
pipe  and  is  not  wasted.  In  the  second 


PACKING 


FIG.  81. — METHODS  OF  PREVENTING  OIL  LEAKS 

method  a  packing  of  soft  material,  such  as 
cotton  or  asbestos,  is  placed  around  the 
plunger,  and  is  pressed  against  it  by  a  gland, 
which  is  like  a  thick  washer.  A  packing  nut 
screws  against  the  gland,  and  thus  squeezes 
the  packing  against  the  plunger. 


192 


TRACTOR  PRINCIPLES 


A  mechanical  lubricator,  or  oiler,  consists 
of  several  small  oil  pumps  placed  in  an  oil 
tank,  each  pump  feeding  one  special  bear- 
ing, and  all  driven  by  the  engine.  Figure 


OILEft 


FIG.  82. — "TITAN"  LUBRICATOR 

82  is  a  top  view  of  a  2-cylinder  horizontal  en- 
gine oiled  by  a  six-feed  oiler.  The  bearings 
that  it  oils  are  the  two  ends  of  the  crank 
shaft,  the  two  ends  of  the  cam  shaft,  and  the 
two  cylinders;  the  gears  and  other  bearings 


LUBRICATION 


193 


are  oiled  by  splash.  An  oiler  is  adjustable, 
so  that  it  will  feed  any  desired  quantity  of 
oH. 

Figure  83  shows  a  side  view  and  an  end 
view  of  the  crank  shaft  of  a  2-cylinder  hori- 
zontal engine.  To  each  end  of  the  crank  is 
attached  a  ring,  B,  formed  into  a  channel; 


FIG.  83. — "I.  H.  C."  METHOD  OP  OILING  CRANK  PINS 

oil  splashing  into  this  ring  is  thrown  into 
the  channel  by  centrifugal  force,  and  flows 
by  holes,  A,  to  the  crank  pin  bearings. 

The  oil  forced  to  the  cylinders  from  the 
oiler,  Figure  82,  reaches  the  wrist  pin  bj 
grooves  and  holes,  A,  Figure  83. 

A  6-feed  oiler  is  also  shown  in  Figure  84. 

Figure  85  is  an  oil  cup,  which  is  used  to 
feed  an  individual  bearing.  It  is  a  glass  cup 
holding  oil  with  an  opening  at  the  bottom 


194 


LUBBICATION 


195 


ADJUSTMENT 


VEWT 


NEEDLE 
VALVE 


SIGHT  GLASS 


BALL  CHECK 

VALVE 


FIG.  85. — OIL  CUP 

into  which  fits  a  needle  valve.  When  the 
engine  is  at  rest,  the  needle  valve  handle 
at  the  top  is  turned  down,  which  allows  a 


THIS  SPACE  SHOULD  8C 
FILLED  WITH  GREASc. 


UNLESS  CUP  IS  PROPERLY  FILLED 

SEVERAL  TURNS  WILL  BE  REOURED 

TO  FORCE  GREASE  ON  BEARING 


^BEARING  SECTION 


CUP  HAS  NOT  BEEN  TURNED 
ENOUGH  TO  FORCE  GREASE  ON 
ENTIRE  BEARING-ONLY  PART  OF 
THE  BEARING  IS  LUBRICATED 


CUP  SHOULD  BE  TURNED  DOWN 

UNTIL  GREASE  APPEARS  AT  THE 

ENDS  OF  BEARING 


FIG.  86. — PROPER  USE  OP  A  GREASE  CUP 
196 


LUBRICATION  197 

spring  to  close  the  needle  valve ;  on  starting 
the  engine  the  needle  valve  is  raised,  and 
the  oil  flows  out  by  gravity.  The  dripping 
oil  may  be  seen  through  a  sight  glass  at  the 
bottom. 

In  the  force  feed  and  oiler  systems  the  oil 
feeds  only  when  the  engine  is  running,  but 
with  an  oil  cup  the  oil  feeds  all  of  the  time 
that  the  needle  valve  is  raised.  Care  must 
therefore  be  taken  to  turn  on  the  oil  cup 
when  starting  the  engine,  and  to  turn  it  off 
when  the  engine  is  stopped. 

Change  speed  gears  and  differentials  are 
usually  enclosed  in  oil-tight  housings  that 
contain  a  supply  of  oil  or  grease.  The  only 
attention  that  is  required  is  to  see  that  they 
have  the  necessary  amount,  and  that  the  lub- 
ricant is  of  the  right  kind. 

The  bearings  of  wheels  and  of  many  other 
parts  of  a  tractor  are  lubricated  with  grease 
fed  by  grease  cups;  a  grease  cup  has  a  cover 

that,  when  screwed  down,  forces  the  grease 

/ 

out  of  a  hole  in  the  bottom  of  the  cup.    In 


200          TRACTOR  PRINCIPLES 

using  a  grease  cup  it  is  not  sufficient  simply 
to  give  the  cover  a  turn  or  two;  the  cover 
should  be  screwed  down  enough  to  force  an 
ample  supply  of  grease  to  the  bearing.  This 
is  illustrated  in  Figure  86. 

Figures  87  and  88  are  oiling  diagrams. 
They  show  the  many  points  at  which  a  trac- 
tor must  be  lubricated,  and  it  should  be  re- 
membered that  the  failure  to  maintain  a  plen- 
tiful supply  of  lubricant  at  any  one  of  these 
points  will  mean  the  wear  and  break-down  of 
that  particular  part. 


CHAPTER  XI 

TKACTOB    OPERATION 

BEFORE  running  a  new  tractor  it  should  be 
given  a  careful  examination  to  make  sure  that 
all  nuts  and  bolts  are  tight,  and  not  secured 
only  by  paint ;  that  all  grease  cups  are  in  po- 
sition and  filled ;  that  all  parts  of  the  mechan- 
ism are  properly  lubricated;  that  oil  holes 
are  free  from  grit,  and  that  nothing  is 
cracked,  broken  or  missing.  It  should  be 
cleaned  of  cinders  and  mud  that  may  have 
collected  in  shipment,  and  in  general  it 
should  be  seen  to  be  in  proper  condition. 

A  tractor,  like  any  other  piece  of  machin- 
ery, requires  breaking  in,  and  for  the  first 
few  days  it  should  be  run  slowly  and  with 
light  loads.  All  parts  should  be  plentifully 
oiled,  for  there  will  be  rough  and  uneven 

places  on  the  bearings  that  must  be  worn 
201 


202          TRACTOR  PRINCIPLES 

smooth,  and  without  oil  these  would  heat  and 
be  injured. 

A  continual  watch  should  be  kept  for  loose 
nuts  and  bolts,  which  should  be  tightened 
without  delay.  Readjustments  of  the  clutch 
and  brake  will  be  found  necessary,  for  their 
linings  when  new  may  be  lumpy;  as  these 
lumps  wear  down  through  use  the  clutch  or 
brake  will  begin  to  slip  and  must  be  tight- 
ened. When  the  linings  are  worn  in,  this 
trouble  will  disappear,  and  readjustments 
will  be  necessary  only  at  considerable  inter- 
vals. 

Special  care  should  be  taken  to  keep  the 
filler  caps  of  the  fuel  and  oil  tanks  clean  and 
free  from  dirt.  If  these  are  dirty,  the  dirt 
will  be  carried  into  the  tank  when  filling,  and 
will  sooner  or  later  cause  trouble. 

The  vent  holes  in  the  filler  caps  should  be 
kept  clear.  If  they  are  plugged  with  dirt, 
air  cannot  enter  the  tank  to  take  the  place  of 
the  fuel  that  flows  out,  and  the  feed  of  fuel 
will  stop. 


TRACTOR  OPERATION          203 

Beginning  when  the  tractor  is  new,  a  sys- 
tem of  daily  inspection  should  be  started,  and 
should  be  continued  for  the  working  season. 
Big  trouble  starts  with  small  trouble,  and 
if  small  trouble  is  cured  without  delay,  big 
trouble  will  be  avoided.  Trouble  usually  be- 
gins with  looseness,  which  may  be  due  to  a 
slack  nut  or  bolt,  or  may  come  with  wear. 
If  the  loose  part  is  not  tightened,  it  will  be- 
gin to  shift  its  position;  it  will  wear,  and  will 
rapidly  lead  to  a  breakdown. 

Every  day,  without  fail,  all  parts  of  the 
tractor  should  be  inspected  for  loose  nuts, 
bolts,  pipe  and  electrical  connections,  pet- 
cocks,  drain  plugs,  steering  connections,  etc. 
This  is  also  the  time  for  wiping  off  the  work- 
ing parts,  and  cleaning  mud  and  grit  from 
rods,  shafts,  joints,  and  other  places  at 
which  dirt  could  make  its  way  into  bearings. 

The  change  speed  gears  of  a  tractor  should 
not  be  shifted  while  in  motion,  this  being  one 
of  the  differences  between  a  tractor  and  an 
automobile.  In  the  sliding  gear  type  of 


204          TRACTOR  PRINCIPLES 

change  speed  mechanism,  the  gears  slide  into 
mesh  sideways,  a  tooth  of  one  being  oppo- 
site a  space  between  two  teeth  of  the  other. 
If  the  gears  are  not  in  the  right  position  for 
this,  one  tooth  will  strike  another,  and  the 
gears  cannot  be  meshed.  In  such  a  case  the 
clutch  is  let  in  for  a  slight  touch  to  move 
one  gear,  not  for  a  dozen  or  twenty  revolu- 
tions, but  enough  to  bring  a  space  between 
two  teeth  of  one  gear  opposite  a  tooth  of  the 
other. 

If  an  attempt  is  made  to  shift  the  gears 
while  they  are  in  motion,  the  result  will  be 
that  one  will  grind  against  the  other,  and 
there  will  be  rapid  wear  and  probable  break- 
age. It  is  because  gears  cannot  be  shifted 
while  they  are  moving  that  manufacturers 
instruct  users  not  to  attempt  to  shift  on  a 
hill  without  first  blocking  the  wheels.  The 
reason  for  this  is  that  the  brakes  may  not 
hold  the  tractor,  and  if  the  gears  are  pulled 
out  of  mesh,  the  machine  may  start  to  run 
down  hill;  as  another  speed  cannot  then  be 


TBACTOR  OPEEATION          205 

engaged  because  the  gears  are  moving,  there 
will  be  no  control  over  the  tractor. 

Never  coast  down  hill;  always  run  with 
one  of  the  speeds  engaged.  By  switching  off 
the  ignition  the  motion  of  the  tractor  will 
drive  the  engine,  and  this  provides  the  best 
possible  brake.  On  low  gear,  the  engine  will 
turn  in  the  neighborhood  of  eighty  revolu- 
tions to  one  turn  of  the  driving  wheels,  and 
the  work  required  to  do  this  will  check  the 
tractor  on  the  steepest  of  practicable  grades. 

A  tractor  is  not  built  for  as  accurate  and 
delicate  steering  as  an  automobile  and  should 
always  be  slowed  in  making  a  turn;  this  is 
especially  true  when  hauling  plows  or  other 
loads  in  the  field.  It  is  difficult  to  control 
the  tractor  if  a  turn  is  made  at  high  speed, 
and  the  machine  is  liable  to  tip  over. 

In  steering  and  in  engaging  the  clutch,  the 
action  should  not  be  jerky  and  abrupt,  but 
gradual  and  smooth.  Letting  in  the  clutch 
suddenly  will  start  the  tractor  with  a  jerk 
that  will  strain  it  from  end  to  end,  and  an 


206          TRACTOR  PRINCIPLES 

abrupt  swing  of  the  steering  wheel  will  have 
the  same  effect.  Making  these  motions 
smoothly  and  steadily  will  cause  the  tractor 
to  change  its  direction  or  pace  with  the  least 
possible  strain  and  effort.  This,  of  course, 
increases  the  tractor's  life. 

In  much  of  the  work  done  by  the  tractor, 
the  varying  conditions  of  field  and  soil  make 
a  continual  change  in  the  load,  and  the  trac- 
tor must  be  handled  accordingly.  The 
change  from  an  uphill  to  a  downhill  haul,  and 
from  sand  or  light  loam  to  gumbo,  will  re- 
quire the  gears  to  be  shifted  in  order  that  the 
engine  may  neither  labor  nor  race  in  keep- 
ing the  outfit  at  its  work. 

There  should  be  no  hesitation  in  coming 
down  to  low  speed  when  the  engine  shows  by 
its  laboring  that  the  effort  of  working  on 
high  gear  is  becoming  too  great.  The  en- 
gine cannot  deliver  its  full  power  unless  its 
speed  is  maintained,  and  low  gear  is  pro- 
vided for  those  times  when  the  load  is  too 
great  to  be  handled  on  high.  Use  high  speed 


TRACTOR  OPERATION          207 

whenever  it  is  possible,  but  trying  to  force 
the  tractor  to  run  on  high  with  too  great  a 
load  will  lead  to  a  breakdown. 

High  speed  should  be  used  for  light  work 
or  for  moving  from  place  to  place,  but  the 
engine  should  never  be  run  at  a  greater  num- 
ber of  revolutions  than  that  specified  by  the 
manufacturers.  It  is  very  poor  policy  to 
run  the  tractor  fast  over  rough  roads,  as  the 
pounding  will  inevitably  injure  it. 

Cold  weather  changes  conditions  in  the 
handling  and  operation  of  a  tractor ;  there  is 
difficulty  in  starting,  lubrication  is  likely  to 
be  faulty,  and  there  is  danger  of  breakage 
in  engine,  radiator,  and  air  washer  through 
freezing. 

Difficulty  in  starting  comes  from  the  use 
of  the  usual  medium  grade  of  gasoline,  which 
is  satisfactory  in  mild  weather,  but  will  not 
vaporize  at  low  temperatures.  Cold  gaso- 
line will  not  vaporize  in  a  cold  engine;  to 
form  a  mixture  it  is  necessary  to  use  high 
test  gasoline,  which  will  vaporize  at  low  tern- 


208          TKACTOE,  PEINCIPLES 

peratures,  or  to  warm  the  engine  to  a  tem- 
perature at  which  medium  grade  gasoline 
will  vaporize. 

It  is  advisable  to  keep  on  hand  a  few  gal- 
lons of  high  test  gasoline  to  use  in  starting, 
or  even  a  mixture  of  high  test  gasoline  and 
ether,  half-and-half,  for  extreme  cold 
weather. 

The  engine  may  be  warmed  by  pouring  a 
bucket  of  hot  water  into  the  cooling  system, 
cranking  the  engine  to  get  it  into  the  water 
jackets  of  the  cylinders.  Another  plan  is  to 
wrap  cloth  around  the  intake  manifold  and 
carburetor,  soaking  it  with  hot  water,  being 
careful  not  to  get  water  into  the  air  intake. 

A  drop  of  liquid  gasoline  on  the  points  of 
the  spark  plug  will  short-circuit  them  and 
prevent  the  formation  of  a  spark;  the  points 
should  be  dry,  and  it  is  an  advantage  to  heat 
the  plugs,  screwing  them  hot  into  the  engine 
at  the  last  moment  before  trying  to  start. 

Kerosene  is  thicker  when  cold  than  when 
warm;  it  will  not  flow  so  freely,  and  the 


TRACTOR  OPERATION          209 

needle  valve  of  the  carburetor  must  be 
opened  more  in  winter  than  in  summer  to 
obtain  a  proper  mixture. 

Lubricating  oil  also  thickens  in  cold 
weather,  and  flows  much  more  sluggishly. 
The  lubrication  adjustments  that  are  correct 
for  summer  will  therefore  be  incorrect  for 
winter.  This  may  be  provided  for  to  a  great 
extent  by  using  a  thinner  oil  in  winter  than 
the  oil  used  in  summer.  A  cold  snap  is 
likely  to  result  in  burned  bearings  if  the 
change  in  lubrication  that  it  brings  is  not  al- 
lowed for. 

Grease  thickens  in  cold  weather  more  than 
oil  does,  and  some  kinds  freeze  solid.  In 
winter  a  light,  soft  grease  should  be  used, 
and  the  grease  cups  should  be  turned  down 
several  more  turns  than  is  usual  when  the 
weather  is  warm. 

While  antifreezing  compounds  can  be  used 
in  the  cooling  systems  of  automobiles,  they 
are  not  suitable  for  tractors  because  the 
greater  and  more  continuous  heat  quickly 


210          TRACTOR  PRINCIPLES 

evaporates  them.  The  danger  of  freezing  is 
very  great,  and  must  be  avoided;  the  water 
in  the  radiator  and  jackets  is  in  thin  sheets, 
and  will  freeze  when  a  bucket  of  water  stand- 
ing in  the  open  will  not  show  any  signs  of 
ice. 

The  only  real  protection  against  freezing 
is  to  drain  out  all  the  water  whenever  the 
tractor  is  to  stand  idle  for  a  sufficient  time 
for  it  to  cool  off.  Petcocks  are  provided  for 
this  at  the  lowest  points  of  the  system,  and 
also  in  the  pump  when  forced  circulation  is 
used.  The  freezing  of  even  a  small  pocket 
of  water  will  be  enough  to  crack  a  cast-iron 
water  jacket  wall,  and  the  best  assurance  that 
the  system  is  thoroughly  drained  is  to  open 
the  drain  cocks  while  the  engine  is  still  run- 
ning, shutting  down  as  the  flow  stops. 

When  putting  up  a  tractor  for  the  winter 
it  should  be  thoroughly  protected  from  rust 
and  corrosion.  The  last  time  that  the  tanks 
are  filled  a  quart  of  light  oil  should  be  added 
for  every  five  gallons  of  gasoline  or  kero- 


TRACTOR  OPERATION          211 

sene;  as  the  tank  empties  this  will  leave  a 
coating  of  oil  on  the  inside  walls. 

Fuel  tanks  and  water  system  should  be 
drained,  and  particular  care  should  be  taken 
that  all  the  water  is  out;  the  drain  cocks 
should  be  left  open.  A  mechanical  oiler 
should  be  filled  full,  to  protect  the  steel  parts 
of  the  pumps  from  rust. 

A  half  pint  of  thick  oil  should  be  put  into 
each  cylinder,  and  spread  to  the  cylinder  and 
piston  walls  by  cranking  for  a  few  turns. 
Oil  should  be  run  between  the  valves  and 
their  seats. 

All  exterior  parts  should  be  protected  by 
a  coat  of  thick  oil  or  by  paint.  The  govern- 
or rod,  push  rods,  and  similar  parts  should 
be  especially  looked  after.  It  is  advisable  to 
take  off  the  magneto  and  store  it  in  a  safe, 
dry  place ;  spark  plugs  should  be  left  in  po- 
sition. 

The  tractor  should  be  covered  with  a  tar- 
paulin and  stored  in  a  tight  shed. 

When  going  over  a  tractor  preparatory  to 


212          TRACTOR  PEINCIPLES 

laying  it  up,  a  list  should  be  made  of  all  parts 
that  need  renewal.  These  parts  should  be 
procured  at  once;  they  are  more  readily  ob- 
tained during  the  winter  than  in  the  operat- 
ing season,  and  will  be  on  hand  for  the  spring 
overhaul. 


CHAPTER  XII 

ENGINE   MAINTENANCE 

FUEL  SYSTEM  AND  CARBURETOR 

THE  operation  of  a  carburetor  depends  on 
so  many  things  that  no  exact  instructions  for 
its  adjustment  can  be  given.  The  best  that 
can  be  done  is  to  give  a  general  idea  of  the 
requirements,  and  to  outline  a  plan  by  which 
the  adjustment  can  be  arrived  at. 

The  many  makes  and  designs  of  carbure- 
tors and  vaporizers  that  are  used  on  tractors 
have  different  kinds  of  adjustments ;  on  most 
of  them  the  only  adjustment  is  the  needle 
valve  that  controls  the  fuel,  but  some  also 
have  adjustable  air  valves.  In  any  case,  the 
manufacturer's  instruction  book  should  be 
studied  for  the  understanding  of  the  particu- 
lar carburetor  in  question. 

213 


214          TEACTOE  PEINCIPLES 

The  first  step  in  adjusting  a  carburetor  is 
to  get  the  engine  running.  The  needle  valve 
should  be  closed,  and  then  opened  enough 
to  give  a  mixture  on  which  the  engine  will 
start ;  on  many  carburetors  this  will  be  about 
one  and  one  half  turns.  The  engine  should 
then  be  primed;  that  is,  a  little  gasoline 
should  be  put  in  the  cylinder,  which  may  be 
done  with  a  squirt  can. 

When  the  engine  is  running,  and  is  well 
heated,  the  needle  valve  should  be  gradu- 
ally closed  until  the  engine  begins  to  miss, 
and  to  send  jets  of  flame  out  of  the  carbure- 
tor, or  little  explosions  occur  in  the  carbure- 
tor. These  are  signs  of  a  thin  mixture,  and 
the  needle  valve  should  be  gradually  opened 
to  make  the  mixture  richer.  The  engine  will 
run  more  steadily,  and  will  pick  up  speed  un- 
til the  mixture  becomes  too  rich,  when  it  will 
choke  and  black  smoke  will  come  out  of  the 
exhaust. 

The  positions  of  the  needle  valve  for  a 
mixture  that  is  too  thin  and  one  that  is  too 


ENGINE  MAINTENANCE         215 

rich  have  thus  been  found,  and  it  remains  to 
set  it  at  that  point  between  at  which  the  en- 
gine runs  most  steadily  and  at  the  best  speed. 

With  adjustable  air  valves  it  is  usual  to 
adjust  for  idling,  that  is,  the  slowest  speed 
at  which  the  engine  will  run  steadily  without 
load,  and  then  to  make  any  necessary  addi- 
tional adjustment  for  full  speed  and  power. 

If  a  carburetor  cannot  be  adjusted  by  fol- 
lowing the  usual  methods,  trouble  may  be 
looked  for,  and  this  may  be  in  the  carburetor 
itself,  in  the  fuel  supply,  or  in  the  intake 
manifold,  taking  for  granted,  of  course,  that 
the  engine  is  in  proper  condition  and  that 
the  ignition  system  is  operating  correctly. 

Dirt  under  the  float  valve  will  prevent  the 
valve  from  seating,  and  the  level  in  the  float 
chamber  will  be  too  high,  so  that  the  mixture 
is  too  rich.  Lifting  the  valve  from  its  seat 
will  let  fuel  rush  through,  and  loose  parti- 
cles will  thus  be  washed  away.  If  dirt  is 
ground  into  the  valve  and  seat,  or  if  these 
parts  are  worn,  the  valve  must  be  reseated, 


216         TRACTOR  PRINCIPLES 

which  is  done  by  turning  the  valve  against 
its  seat  with  light  pressure,  the  end  of  the 
valve  being  gently  tapped  with  a  light  ham- 
mer. Under  no  conditions  use  a  grinding 
compound,  for  the  particles  would  become 
imbedded  in  the  soft  metal  and  would  ruin 
the  valve. 

Other  causes  of  flooding  are  a  bent  valve, 
the  sticking  of  the  float  pivot,  and  the  soak- 
ing of  fuel  into  the  cork  float,  which  is  thereby 
made  too  heavy  to  float  properly.  The  rem- 
edy is  to  dry  it,  and  then  to  give  it  three 
coats  of  shellac. 

A  frequent  cause  of  trouble  is  dirt  in  the 
pipe  from  the  tank  to  the  carburetor.  While 
there  may  not  be  enough  dirt  to  prevent  the 
engine  from  running  slowly,  it  is  sufficient 
to  prevent  the  flow  of  sufficient  fuel  for  full 
power.  A  strainer  is  always  provided,  and 
this  should  be  drained  every  day;  if  this  is 
not  done  frequently,  dirt  will  work  its  way 
through. 

A  grain  of  sand  in  the  spray  nozzle  will 


ENGINE  MAINTENANCE         217 

choke  it,  and  every  precaution  should  be 
taken  to  keep  this  from  happening,  as  well 
as  the  other  troubles  that  dirt  brings.  The 
best  precaution  is  to  strain  the  fuel  through 
chamois  leather,  or,  if  this  is  not  obtainable, 
through  a  very  fine  metal  wire  screen. 

In  fuel  systems  that  use  a  pump,  the  stick- 
ing of  the  check  valves,  and  the  leaking  of 
the  pump  through  poor  packing,  will  cut 
down  the  supply  of  fuel. 

If  air  can  leak  into  the  carburetor  or  in- 
take manifold,  the  proportions  of  the  mixture 
will  be  altered.  To  test  for  leaks,  run  the 
engine,  and  with  a  squirt  can  squirt  gaso- 
line on  the  joints  or  other  places  that  are 
suspected  of  leaking  air.  If  there  is  a  leak, 
the  gasoline  can  be  seen  being  sucked  in. 

Air  must  enter  the  tank  to  take  the  place 
of  the  fuel  that  flows  out,  and  this  is  pro- 
vided for  by  a  small  hole  drilled  in  the  tank- 
filling  cap.  If  this  hole  becomes  stopped  up, 
the  fuel  will  not  flow,  and  the  engine  will 
come  to  a  stop.  There  is  a  similar  hole  in 


218          TEACTOE  PEINCIPLES 

the  top  of  the  float  bowl  of  most  carburetors, 
and  this  also  must  be  kept  open. 

An  engine  is  always  started  on  gasoline, 
for  that  will  form  a  mixture  when  it  is  cold. 
Before  switching  to  kerosene  the  engine  must 
be  hot,  and  this  will  take  several  minutes  of 
running  on  gasoline. 

With  a  double  carburetor,  which  has  a 
separate  fuel  bowl  and  spray  nozzle  for  each 
fuel,  nothing  more  is  required  than  the 
switching  of  one  or  the  other  into  action; 
when  the  two  parts  have  once  been  adjusted, 
they  require  no  further  adjustment.  Car- 
buretors that  use  the  same  spray  nozzle  for 
both  gasoline  and  kerosene  will  require  a  re- 
adjustment when  the  switch  is  made,  for,  as 
kerosene  is  thicker  than  gasoline,  it  will  re- 
quire a  larger  opening  for  a  sufficient  quan- 
tity to  pass.  This  readjustment  is  a  slight 
opening  of  the  needle  valve  on  switching  to 
kerosene,  and  an  equal  closing  when  gaso- 
line is  again  used. 

A  few  minutes  before  the  engine  is  stopped 


ENGINE  MAINTENANCE        219 

the  carburetor  should  be  switched  from  kero- 
sene to  gasoline,  so  that  when  it  is  shut  down 
the  fuel  bowl  will  contain  gasoline  and  the 
cylinders  gasoline  mixture.  This  is  done  to 
make  it  possible  to  start  the  engine.  If  the 
engine  is  stopped  on  kerosene,  it  cannot  be 
started  if  it  has  had  time  to  cool.  In  such 
a  case  the  fuel  bowl  must  be  drained  of  kero- 
sene and  filled  with  gasoline,  and  the  engine 
must  be  cranked  until  the  cylinders  receive 
a  clean  gasoline  mixture. 

When  an  engine  is  working  at  full  power 
on  kerosene,  it  gets  much  hotter  than  would 
be  the  case  with  a  gasoline  mixture.  Car- 
bon particles  in  the  cylinder,  and  project- 
ing bits  of  metal,  such  as  thin  spark  plug 
points  or  the  edge  of  a  screw  thread,  become 
so  hot  that  they  glow,  with  the  result  that 
they  ignite  the  incoming  fresh  charge  and 
cause  preignition.  The  effect  of  this  is  to 
cause  a  pounding  or  knocking  that  is  very 
noticeable.  It  is  then  necessary  to  use  water, 
which  is  provided  for  in  the  carburetor. 


220          TRACTOR  PRINCIPLES 

Water  has  the  effect  of  cooling  the  in- 
tensely heated  parts,  and  only  enough  should 
be  used  to  prevent  preignition.  When  the 
knocking  is  heard,  water  should  gradually 
be  turned  on,  using  no  more  than  is  neces- 
sary to  stop  the  noise.  Too  much  water  will 
cause  the  engine  to  miss  by  collecting  on  the 
spark  plug  points,  thereby  preventing  the 
passing  of  the  ignition  spark. 

Hard  water  should  not  be  used,  for  it  will 
form  scale,  which  will  interfere  with  the  ac- 
tion of  the  carburetor.  Only  soft  water 
should  be  used,  and  preferably  rain  water. 

Whenever  the  engine  is  stopped,  the  fu;l 
valve  at  the  tank  should  be  closed  to  shut  off 
the  carburetor  supply.  If  this  is  not  done, 
the  float  valve  will  be  the  only  thing  that  pre- 
vents the  fuel  from  running  out,  and  should 
the  float  valve  leak,  the  fuel  will  be  wasted. 

MAGNETO  AND  IGNITION  SYSTEM 

A  magneto  that  is  kept  clean  and  prop- 
erly oiled  rarely  gives  trouble,  and  it  is  a 


ENGINE  MAINTENANCE         221 

mistake  to  blame  it  whenever  the  engine  runs 
irregularly  or  will  not  start.  Its  adjust- 
ments should  be  changed  only  when  the  other 
parts  of  the  engine  have  been  proved  to  be 
in  good  condition. 

The  working  parts  of  a  magneto  are  en- 
closed, and  practically  proof  against  dust. 
It  should  be  wiped  off  frequently,  and  dust 
and  grit  should  not  be  allowed  to  collect 
around  the  oil  holes,  for  otherwise  it  will 
work  into  the  bearings  and  damage  them. 

Dust  and  dirt  are  especially  injurious  to 
the  circuit  breaker,  which  should  be  fre- 
quently inspected  and  cleaned.  Very  little 
oil  should  be  used  on  it,  and  this  should  be 
the  light  oil  used  for  typewriters  and  sewing 
machines.  A  thicker  oil  will  become  gummy, 
and  will  prevent  the  free  action  of  the  lever. 

If  there  is  much  sparking  at  the  platinum 
points,  so  that  they  become  corroded  and 
rough,  it  is  an  indication  that  the  condenser 
of  the  magneto  is  not  operating  as  it  should, 
for  the  object  of  the  condenser  is  to  prevent 


222          TRACTOR  PRINCIPLES 

such  sparking.    The  only  remedy  is  to  renew 
the  condenser. 

Rough  points  will  spark  more  than  smooth 
ones ;  should  they  get  into  this  condition,  they 
should  be  lightly  filed  with  a  file  of  the  cut 
known  as  "dead  smooth."  If  this  file  can- 
not be  obtained,  pinch  a  strip  of  the  finest 
sand  paper — not  emery  paper — between  the 
points,  and  draw  it  gently  back  and  forth, 
smoothing  down  first  one  point  and  then  the 
other.  In  smoothing  platinum  points  the 
greatest  care  should  be  taken  to  make  them 
flat  and  true  to  each  other. 

After  smoothing  the  points  they  should  be 
readjusted  so  that  when  they  are  separated 
by  the  cam  they  are  from  1/32  to  1/64  inch 
apart. 

A  distributor  made  with  a  carbon  brush 
that  slides  across  the  contacts  will  require 
wiping  off  at  least  once  a  month.  Carbon 
dust  will  rub  off  the  brush  and  collect  on  the 
face  of  the  distributor;  in  the  course  of  time 
this  will  cause  a  short  circuit.  The  distribu- 


ENGINE  MAINTENANCE        223 

tor  is  always  made  so  that  it  can  easily  be 
cleaned. 

A  magneto  is  timed  to  an  engine  so  that 
when  the  spark  control  is  fully  retarded,  the 
circuit  breaker  points  are  just  separating  as 
a  piston  goes  over  top  center.  The  engine 
is  cranked  until  one  of  the  pistons  is  at  top 
center;  the  magneto  should  be  in  position, 
but  its  coupling  should  be  loose,  so  that  the 
armature  can  be  revolved.  The  spark  con- 
trol is  retarded ;  that  is,  it  is  moved  as  far  as 
possible  in  the  direction  in  which  the  arma- 
ture turns.  The  armature  is  then  revolved 
in  the  direction  in  which  it  will  be  driven  by 
the  engine  until  it  is  seen  that  the  contact 
points  are  beginning  to  separate ;  holding  the 
armature,  the  coupling  is  then  made  fast. 

It  will  now  be  found  that  the  distributor 
brush  is  touching  one  of  the  contacts;  that 
contact  is  to  be  connected  with  the  spark  plug 
of  the  cylinder  that  is  at  top  center  of  the 
compression  stroke.  The  following  distribu- 
tor contacts  are  connected  to  the  remaining 


224          TRACTOR  PRINCIPLES 

spark  plugs  in  the  order  in  which  their  cyl- 
inders fire. 

Should  the  magneto  be  suspected  of  being 
out  of  order,  the  first  test  is  to  disconnect  a 
wire  from  its  spark  plug,  and  support  the 
tip  y8  inch  from  the  metal  of  the  engine  while 
the  engine  is  cranked  briskly;  if  a  spark  ap- 
pears, it  is  evidence  that  the  magneto  is  op- 
erating and  that  the  trouble  is  elsewhere. 

If  there  is  no  spark,  repeat  the  test  with 
the  switch  wire  disconnected  from  the  mag- 
neto. This  wire  and  the  switch  form  a  cir- 
cuit from  the  metal  of  the  engine  to  the  in- 
sulated part  of  the  circuit  breaker ;  when  the 
switch  is  closed,  or  in  the  "off"  position,  this 
circuit  is  completed,  and  as  the  magneto  cur- 
rent flows  over  it  instead  of  over  the  regular 
sparking  circuit,  no  spark  is  produced  at  the 
plug.  It  sometimes  happens  that  the  switch 
or  wire  is  defective,  and  allows  the  current  to 
take  that  circuit  even  when  the  switch  is  in 
the  open  or  "run"  position.  If  this  is  the 
case  it  will  be  shown  by  a  spark  on  cranking 


ENGINE  MAINTENANCE        225 

the  engine  with  the  switch  wire  disconnected 
at  the  magneto,  and  no  spark  when  it  is  con- 
nected. 

If  the  switch  and  wire  are  all  right,  exam- 
ine the  circuit  breaker  to  see  whether  the 
contact  points  are  clean,  and  that  they  touch 
when  the  cam  allows  them  to;  touch  the  cir- 
cuit breaker  lever  to  see  that  it  is  free  to 
move  and  that  its  spring  is  not  broken.  In 
some  tractors  the  magneto  is  in  such  a  posi- 
tion that  the  circuit  breaker  cannot  easily 
be  seen;  in  such  a  case  hold  a  small  mirror 
in  front  of  the  circuit  breaker  and  examine 
the  reflection. 

If  the  circuit  breaker  is  in  good  condition, 
examine  the  distributor  to  see  whether  it  is 
dirty,  or  the  brush  broken ;  if  these  parts  are 
all  right,  the  trouble  is  of  such  a  character 
as  requires  the  magneto  to  be  returned  for 
repair. 

Ignition  trouble  is  usually  in  the  spark 
plugs.  The  insulator  cracks  easily  in  many 
makes,  which  will  permit  the  current  to  leak 


226          TRACTOR  PRINCIPLES 

across  without  forming  a  spark;  it  is  fre- 
quently the  case  that  the  crack  does  not  show, 
and  the  best  test  is  to  replace  the  suspected 
plug  with  a  plug  that  is  known  to  be  good. 
If  the  cylinder  fires  with  one  plug  and  not 
with  the  other,  there  is  no  question  as  to  the 
cause  of  the  trouble. 

The  insulator  of  the  plug  must  be  kept 
clean,  for  a  deposit  of  carbon  on  it  will  form 
a  path  by  which  the  current  can  pass  with- 
out forming  a  spark.  A  dirty  plug  can  best 
be  cleaned  by  brushing  it  with  a  stiff  tooth- 
brush dipped  in  gasoline.  A  carbon  deposit 
can  be  softened  by  soaking  the  plug  in  gaso- 
line for  a  few  hours,  and  can  then  be  brushed 
off  more  easily. 

The  spark  gap  of  a  plug  should  be  from 
1/32  to  1/64  inch.  After  considerable  use  the 
points  will  be  burned  off,  and  the  gap  will 
become  too  wide;  the  points  should  then  be 
bent  to  form  a  proper  gap. 

Oil  and  grease  will  rot  rubber,  and  the  ig- 
nition wires  should  therefore  be  wiped  clean. 


ENGINE  MAINTENANCE        227 

Oil-soaked    cables    will    give    trouble,    and 
should  be  replaced  with  new  ones. 

It  is  frequently  difficult  to  locate  a  leak- 
age of  current.  If  the  engine  is  misfiring 
and  losing  power,  and  a  leakage  of  current 
through  poor  insulation  is  suspected,  the 
easiest  way  to  detect  it  is  to  run  the  engine 
in  the  dark.  Leaks  will  show  themselves  by 
sparks,  which  are  then  easily  seen. 

COMPRESSION 

In  order  to  deliver  its  full  power  a  gas 
engine  must  have  good  compression,  and 
compression  should  frequently  be  tested  by 
cranking  the  engine  slowly  and  steadily  with 
the  ignition  switched  off.  If  compression  is 
good,  there  will  be  a  springy,  elastic  resist- 
ance that  becomes  greater  as  a  piston  ap- 
proaches the  end  of  a  compression  stroke, 
and  that  throws  the  piston  outward  as  dead 
center  is  passed.  Compression  should  be 
the  same  for  all  cylinders. 

If  there  is  a  leakage  of  compression,  the 


228          TRACTOR  PRINCIPLES 

only  resistance  will  be  from  the  bearings, 
and  it  will  be  the  same  for  all  parts  of  the 
stroke. 

A  compression  leak  often  makes  a  hissing 
noise  that  can  be  distinctly  heard,  and  by 
which  it  can  be  located,  but  more  often  it 
makes  no  sound,  and  its  location  must  be 
found  by  testing.  The  leak  may  be  at  any 
of  the  openings  into  the  combustion  space; 
at  the  valves,  around  the  spark  plugs  or  pis- 
ton rings,  or  at  the  cylinder  head  gasket. 

To  discover  whether  the  gasket  leaks,  run 
gasoline  along  the  line  of  the  gasket  joint 
with  a  squirt  can  while  the  engine  is  being 
cranked  briskly;  at  a  leaky  place  it  will  be 
sucked  in  or  blown  out.  The  same  test 
should  be  made  around  the  spark  plug. 

The  remedy  is  to  reset  the  cylinder  head, 
using  a  new  gasket,  and  being  sure  that  the 
surfaces  are  clean  and  free  from  grit. 

Piston  ring  leaks  are  usually  caused  by 
the  rings  sticking  in  their  grooves  through 
the  formation  of  carbon.  To  test  for  piston 


ENGINE  MAINTENANCE         229 

ring  leaks,  pour  a  half  pint  of  cylinder  oil 
into  each  cylinder,  and  crank  the  engine 
slowly.  The  oil  will  form  a  seal  around  the 
pistons,  and  if  compression  is  then  im- 
proved, the  rings  are  shown  to  be  at  fault. 

To  free  the  rings,  pour  a  few  tablespoon- 
fuls  of  kerosene  into  each  cylinder,  and 
spread  it  by  giving  the  engine  a  few  turns; 
after  standing  for  an  hour  or  so  the  carbon 
should  be  sufficiently  softened  to  free  the 
rings. 

If  the  leakage  of  compression  is  due  to  the 
rings  being  worn  and  loose  in  their  grooves, 
they  must  be  replaced. 

The  most  usual  cause  of  compression  loss 
is  leaking  valves.  With  its  continual  pound- 
ing against  its  seat,  and  the  heat  to  which 
it  is  exposed,  a  valve  and  its  seat  will  become 
rough  and  pitted,  and  will  leak ;  when  in  this 
condition  the  valve  must  be  ground. 

A  valve  is  ground  by  spreading  grinding 
compound  on  the  seat,  and  turning  the  valve 
against  it.  This  requires  the  valve  spring 


230         TRACTOR  PRINCIPLES 

to  be  taken  off;  the  exact  method  of  doing 
this  depends  on  how  these  parts  are  made. 

If  the  valves  are  in  a  removable  cylinder 
head,  valve  grinding  is  most  easily  done  by 
taking  the  cylinder  head  to  a  bench.  In 
many  designs  the  valve  seats  are  part  of  the 
cylinder  casting,  and  the  job  is  done  on  the 
tractor. 

In  grinding  a  valve  the  valve  is  not  turned 
around  in  one  direction  only,  for  this  would 
cut  grooves  in  the  valve  and  seat.  To  obtain 
smooth  surfaces  the  valve  should  be  given 
part  of  a  turn  in  one  direction,  and  then 
turned  equally  in  the  other  direction;  after 
every  few  turns  the  valve  should  be  lifted  and 
dropped  to  another  position  on  the  seat.  In 
this  way  the  grinding  is  made  even  all  around. 

The  best  tool  for  valve  grinding  is  a  car- 
penter's brace  with  a  screw  driver  blade  fit- 
ting the  slot  in  the  valve,  as  shown  in  Figure 
89.  This  drawing  illustrates  a  cylinder  with 
a  fixed  head;  the  valve  is  reached  by  un- 
screwing the  plug  from  the  opening  directly 


ENGINE  MAINTENANCE        231 

above  it.    When  grinding  valves  in  an  en- 
gine of  this  design  the  opening  between  the 


VALVE  SCAT 

LIGHT  SPRING  FOR 
LIFTING  VALVE.  OFF 
SEAT  WHEN  GRINDING 


FIG.  89. — GRINDING  VALVE  IN  ENGINE  WITH  FIXED  HEAD 

valve  pocket  and  the  combustion  space  should 
be  plugged  with  a  rag  or  waste  to  prevent 


232          TRACTOR  PRINCIPLES 

the  grinding  compound  from  getting  into  the 
cylinder. 

With  the  valve-grinding  tool  in  position, 
swing  the  handle  back  and  forth  ten  or 
twelve  times;  then  lift  the  valve,  place  it  in 
a  new  position,  and  repeat.  The  valve  is 
lifted  most  easily  by  a  light  spring  placed 
under  the  valve  disk,  as  shown  in  Figure  89. 

From  time  to  time  the  valve  disk  and  seat 
should  be  cleaned  off  and  examined  to  see 
whether  they  are  smooth  and  free  from  pits 
and  scores.  If  they  appear  to  be,  make 
marks  around  the  valve  disk  with  a  lead  pen- 
cil, replace  the  valve,  and  give  it  a  complete 
turn.  If  this  wipes  off  the  pencil  marks  all 
around  the  valve,  the  grinding  is  complete, 
and  the  valve  may  be  replaced  with  its  spring 
and  spring  retainer.  It  is  not  necessary  to 
grind  until  the  entire  thickness  of  the  valve 
disk  and  seat  are  smooth;  a  narrow  band 
all  around  will  make  the  valve  tight. 

After  grinding,  and  before  replacing  the 
valve,  all  traces  of  the  grinding  compound 


ENGINE  MAINTENANCE        233 

should  be  wiped  off,  and  great  care  taken 
that  none  of  it  gets  into  the  cylinder,  valve 
stem  guide,  or  other  working  part. 

On  an  engine  with  a  removable  head  con- 
taining the  valves,  the  head  may  be  taken  to 
a  work  bench,  which  makes  grinding  easier. 


FIG.  90. — GRINDING  VALVE  IN  DETACHABLE  HEAD 

This  is  illustrated  in  Figure  90.  On  an  en- 
gine in  which  the  valve  and  its  seat  may  be 
taken  out,  the  seat  may  be  clamped  in  a  vise, 
as  shown  in  Figure  91.  With  valves  of 
either  of  these  types,  the  grinding  may  be 
tested  by  turning  the  head  or  the  seat  so  that 
the  disk  is  down,  and  pouring  in  gasoline.  If 


234 


TRACTOR  PRINCIPLES 


the  valve  is  not  tight,  the  gasoline  will  leak 
through,  and  grinding  must  be  continued. 

When  a  valve  seat  is  very  badly  worn  it 
must  be  redressed,  which  is  done  with  a  cut- 
ting tool  to  be  obtained  from  the  maker  of 
the  tractor,  and  illustrated  in  Figure  92.  This 
has  a  stem  fitting  the  valve  stem  guide  which 


FIG.  91. — GRINDING  VALVE  IN  DETACHABLE  SEAT 

centers  the  tool  and  assures  a  true  cut.  If  a 
seat  is  so  worn  as  to  need  redressing,  the 
valve  will  be  in  such  bad  condition  that  it 
must  be  discarded  and  a  new  one  used.  This 
must  be  ground  in  before  the  engine  is  run. 
Grinding  a  valve  lowers  it  in  its  seat,  and 
usually  makes  it  necessary  to  readjust  the 
push  rod.  When  an  engine  is  cold  there  is 
a  space  of  about  1/32  inch  somewhere  between 


ENGINE  MAINTENANCE 


235 


the  cam  and  the  valve  stem ;  in  Figure  93,  this 
space  is  shown  to  be  between  the  valve  stem 


FIG.  92. — VALVE  SEAT  CUTTER 

and  the  rocker  arm.  As  the  engine  heats  up 
the  valve  stem  lengthens,  and  this  space  per- 
mits it  to  do  so. 


A// 


236         TRACTOR  PRINCIPLES 

If  the  space  is  too  small,  the  stem  will  come 
against  the  rocker  arm  or  the  push  rod,  and 

the  valve  will 
be  held  off  its 
seat,  causing  a 
compression 
leak.     If     the 
space    is    too 
great,    the 
valve  will  op  en 
too    late    and 
close  too  early. 
The    space 
must    there- 
fore be   care- 
fully adjusted, 
and  this  is  ar- 
ranged for  on 
practically  all 
makes  of  trac- 
tor engines. 
One- thirty- 


second    of   an 
FIG.  93. — "  HOLT "  VALVE  ARRANGEMENT  inch     is     the 


ENGINE  MAINTENANCE        237 

thickness  of  a  10-cent  piece ;  it  should  just  be 
possible  to  slip  a  slightly  worn  dime  into  the 
space  when  the  engine  is  cold. 

VALVE  TIMING 

By  timing  the  valves  is  meant  the  setting 
of  the  cam  shaft  in  such  a  position  that  the 
valves  are  opened  at  the  correct  point  in  the 
stroke.  It  is  necessary  to  time  the  valves 
only  when  the  cam  shaft  has  been  taken  out 
and  must  be  replaced.  The  principle  of  valve 
timing  should  be  understood,  however,  in 
order  to  be  able  to  tell  whether  an  engine  is 
timed  correctly. 

It  will  usually  be  found  that  the  face  of  the 
flywheel  bears  letters  and  figures  that  are 
indicators  of  the  timing  of  the  valves.  This 
arrangement  on  the  E-B  engines  is  shown 
in  Figure  94.  Two  lines  are  cut  in  the  face 
of  the  flywheel,  one  marked  ex.  cl.  1-4,  which 
means  exhaust  valve  closes,  cylinders  1  and  4, 
and  the  other  marked  CENTER  1-4,  to  indicate 
that  the  pistons  in  those  cylinders  are  on  cen- 


FINISHED 
SURFACE  Of 
HOUSING 


SCALE  OR  STRAIGHT- EDGE  EXTENDS 
DIAGONALLY  FROM  FINISHED  SUR- 
FACE TO  EDGE  OF  FLY-WHEEL. 


FIRING  POINT  WHEN  MAGNETO 
IS  ON  FULL  ADVANCE 


.  94. — VALVE  TIMING,  USING  MARKS  ON  FLYWHEEL 
238 


ENGINE  MAINTENANCE 


239 


ter.  A  straight-edge  is  held  against  the  fin- 
ished surface  of  the  housing  and  the  crank 
shaft  is  turned  to  bring  one  of  the  marks  in 


AOJUSTIN9  SCRttW  JU»Y 
TOUCHES  VAUVE  STtW 
L.OC.K  NUT 

EXHAUST  VAUVC  UIPT 
SLIGHTLY  HAISED 
XHAUST  CAM 


SHAFT  e,t AR 


FIG.  95. — VALVE  TIMING 


line  with  it;  at  that  point  the  valves  or  pis- 
tons are  as  indicated  by  the  lettering. 
The  flywheel  is  also  marked  with  a  dot  to 


240          TRACTOR  PRINCIPLES 

indicate  the  firing  point.  When  the  dot  is 
in  line  with  the  straight-edge,  ignition  should 
occur  with  the  spark  control  fully  advanced. 

Figure  95  shows  the  valve  arrangement  of 
the  same  engine,  with  the  exhaust  valve  just 
closing;  the  point  of  the  cam  has  passed  un- 
der the  lifter  or  push  rod,  and  has  permitted 
the  valve  to  come  to  its  seat,  but  is  still  hold- 
ing the  lifter  against  the  valve  stem. 

To  check  the  valve  setting,  hold  a  slip  of 
tissue  paper,  such  as  a  cigarette  paper,  in 
the  space  between  the  lifter  and  the  valve 
stem,  while  the  engine  is  cranked  slowly. 
While  the  cam  is  holding  the  valve  off  its 
seat  the  paper  will  be  pinched  between  the 
lifter  and  the  valve  stem  and  held  firmly.  At 
the  instant  when  the  paper  is  freed  and  can 
be  moved,  the  valve  is  seated  and  the  point 
of  the  cam  is  just  passing  from  under;  the 
proper  mark  on  the  flywheel  should  then  be  in 
line  with  the  straight-edge. 

As  the  cams  for  all  valves  are  in  one  piece 


ENGINE  MAINTENANCE         241 

with  the  cam  shaft,  setting  one  valve  sets 
them  all  and  checking  the  setting  of  one 
checks  the  setting  of  all. 

Before  taking  out  a  cam  shaft,  two  adjoin- 
ing teeth  of  its  gear  should  be  marked  with 
a  prick  punch  or  a  small  cold  chisel,  and  a 
similar  mark  should  be  made  on  the  tooth  of 
the  crank  shaft  gear  that  comes  between 
them.  In  replacing  the  cam  shaft  it  is  then 
necessary  only  to  return  the  teeth  to  the  same 
position.  Timing  gears  are  usually  marked 
in  this  way  by  the  manufacturers. 

CARBON 

A  kerosene  lamp  that  is  turned  too  high 
gives  a  dense  black  smoke  that  is  composed 
of  fine  particles  of  carbon.  A  piece  of  paper 
held  in  the  smoke  is  quickly  covered  with  a 
deposit  of  carbon,  commonly  called  soot,  or 
lamp-black. 

All  fuel  oils  and  lubricating  oils  contain 
carbon.  When  these  oils  burn  in  the  cylin- 
der, they  produce  carbon,  much  of  which 


242          TRACTOR  PRINCIPLES 

passes  out  of  the  exhaust,  while  the  rest  de- 
posits on  the  valves  and  on  all  parts  of  the 
combustion  space.  This  deposit  hardens,  and 
eventually  makes  trouble  through  causing 
preignition. 

The  deposit  is  rough,  and  the  heat  in  the 
cylinder  is  sufficient  to  make  the  outstanding 
particles  glow;  they  ignite  the  incoming 
charge,  and  cause  preignitioiu  The  sign  of 
carbon  trouble  is  a  sharp  knocking  in  the 
cylinder,  especially  when  the  engine  is  under 
a  heavy  load.  The  sound  is  the  same  as  that 
caused  by  too  great  an  advance  of  the  spark. 

Carbon  deposit  can  be  greatly  reduced  by 
pouring  a  few  tablespoonfuls  of  kerosene  into 
each  cylinder  and  cranking  for  a  few  turns  to 
spread  it  to  all  parts  of  the  combustion  space. 
This  will  soften  the  carbon  and  much  of  it 
will  be  blown  out  when  the  engine  is  next 
started.  Best  results  will  be  obtained  if  the 
kerosene  is  poured  in  after  a  run,  when  the 
engine  is  hot. 

If  the  carbon  deposit  is  too  hard  to  be 


ENGINE  MAINTENANCE         243 

softened  by  kerosene,  it  can  be  removed  by 
scraping.  This  requires  the  cylinder  head  to 
be  taken  off,  when  the  deposit  can  be  scraped 
and  chipped  with  a  screwdriver.  Care  should 
be  taken  to  keep  the  carbon  crumbs  from  get- 
ting into  the  cylinders,  valve  stem  guides,  or 
other  places  where  it  would  cause  wear. 

In  taking  off  the  cylinder  head  the  gasket 
should  be  handled  carefully,  and  protected 
from  denting  and  bending.  A  battered  or 
bent  gasket  is  a  sure  cause  of  compression 
leaks.  In  replacing  a  metal  gasket,  give  it 
a  coat  of  cylinder  oil  on  both  sides  to  improve 
its  seating. 

When  replacing  the  cylinder  head,  set  all 
of  the  bolts  up  a  little  at  a  time,  instead  of 
screwing  some  of  them  tight  while  others  are 
loose.  One  bolt  drawn  tight  may  tilt  the  cyl- 
inder head  slightly,  and  there  will  be  a  dis- 
tortion when  another  bolt  is  tightened.  This 
is  avoided  by  setting  up  all  of  the  bolts  a 
little  at  a  time. 

Eunning  on  too  rich  a  mixture,  giving  the 


244         TRACTOR  PRINCIPLES 

engine  too  much  oil,  and  not  using  an  air 
cleaner  in  dusty  work  will  carbonize  an  en- 
gine rapidly.  Blue  smoke  at  the  exhaust  is 
a  sign  that  too  much  lubricating  oil  is  being 
used;  black  smoke  indicates  too  rich  a  mix- 
ture. Carbonizing  can  be  greatly  reduced 
by  careful  adjustment  of  the  lubricator  and 
carburetor. 


CHAPTER 

LOCATING  TROUBLE 

THERE  are  many  ways  in  which  an  engine 
can  give  trouble,  but  these  are  not  serious  to 
an  operator  who  understands  the  action  of 
an  engine,  and  who  works  with  his  brain  as 
well  as  with  his  hands.  Each  of  these  trou- 
bles has  a  distinct  cause;  proper  care  will 
avoid  them,  but  if  they  come  the  reasons  for 
them  can  be  determined  by  simple  tests. 

In  order  to  develop  full  power,  an  engine 
must  be  in  good  mechanical  condition;  that 
is,  the  bearings  must  be  free  without  being 
loose,  the  gears  must  run  well,  the  pistons 
and  their  rings  must  not  bind  or  be  too  free, 
and  so  on.  It  must  be  properly  lubricated 
and  cooled,  compression  must  be  correct,  it 
must  get  a  good  mixture,  and  ignition  must 
take  place  at  the  right  time.  If  an  engine 

245 


246         TRACTOR  PRINCIPLES 

gives  trouble,  it  is  because  one  of  these  sys- 
tems is  not  working  properly,  and  it  is  not 
at  all  difficult  to  locate  the  cause  and  to  cor- 
rect it. 

If  an  engine  gets  a  good  mixture,  which  is 
ignited  properly,  it  will  run;  if  it  will  not 
give  any  explosions  it  is  because  one  or  the 
other  of  these  systems  is  not  working  prop- 
erly. An  inspection  or  a  simple  test  will 
show  which  one  is  at  fault. 

ENGINE  WILL  NOT  START 

If  an  engine  will  not  start  after  being 
cranked  a  dozen  or  twenty  times,  it  is  useless 
to  continue  to  crank  it.  It  is  not  getting 
either  a  proper  mixture  or  an  ignition  spark, 
and  it  saves  time  and  energy  to  find  out 
where  the  trouble  is,  rather  than  to  keep  on 
cranking  in  the  hope  that  something  may 
happen. 

When  a  tractor  engine  refuses  to  start,  the 
trouble  is  usually  with  the  mixture,  and,  more 
often  than  not,  this  is  due  to  carelessness  or 


LOCATING  TROUBLE  247 

to  forgetfulness.  The  tank  may  be  empty, 
or  the  fuel  valve  may  be  closed,  so  that  the 
carburetor  is  dry;  see  if  there  is  fuel  in  the 
carburetor  bowl.  The  engine  may  have  been 
shut  down  while  running  on  kerosene,  instead 
of  having  been  switched  to  gasoline  for  the 
last  few  minutes  of  its  run,  so  that  the  carbu- 
retor, intake  manifold  and  cylinders  contain 
kerosene,  which  will  not  vaporize  without 
heat,  instead  of  gasoline,  which  will.  In  this 
case  the  engine  must  be  primed  with  gasoline. 

If  too  much  gasoline  has  been  used  for 
priming,  the  cylinders  may  contain  a  mixture 
that  is  too  rich  to  ignite;  the  engine  should 
then  be  cranked  briskly  with  the  fuel  shut 
off  and  the  compression  relief  cocks  open,  to 
clear  out  the  rich  mixture  and  fill  the  cylin- 
ders with  air. 

Water  in  the  fuel  will  make  starting  diffi- 
cult or  impossible.  It  is  easy  to  forget  to  shut 
off  the  water  valve  of  the  carburetor  when 
stopping  the  engine,  and  when  starting,  water 
from  this  valve  will  prevent  the  forming  of  a 


248          TRACTOR  PRINCIPLES 

mixture  and  will  also  interfere  with  the  igni- 
tion. 

If  the  mixture  is  apparently  all  right,  the 
fault  may  be  in  the  ignition.  A  drop  of  liquid 
fuel  or  of  water,  for  instance,  may  be  on  the 
spark  plug  points ;  this  will  short-circuit  them 
and  no  spark  will  be  formed,  although  the 
sparking  current  is  passing. 

If  there  is  a  suspicion  that  the  ignition  sys- 
tem is  at  fault,  and  that  the  magneto  is  not 
producing  a  sparking  current,  it  should  be 
tested,  as  explained  in  Chapter  XII. 

Starting  in  cold  weather  is  always  more 
difficult  than  starting  when  it  is  warm.  Helps 
in  cold  weather  starting  are  given  in  Chap- 
ter XL 

A  leaky  inlet  manifold  will  admit  an  extra 
amount  of  air  that  will  completely  alter  the 
proportions  of  a  mixture.  Thus  the  mixture 
will  be  wrong,  although  the  carburetor  ad- 
justment seems  to  be  correct.  Manifold  leaks 
are  usually  at  the  joints,  but  occasionally  a 


LOCATING  TROUBLE  249 

manifold  is  found  with  a  hole  in  it  due  to  poor 
casting  or  material,  or  a  crack  may  develop. 

Difficulty  in  starting  due  to  poor  compres- 
sion caused  by  stuck  valves  or  rings  will  show 
its  cause  by  the  ease  with  which  the  engine 
can  be  cranked. 

If  an  engine  is  free  enough  to  turn  over, 
poor  lubrication  or  cooling  will  not  interfere 
with  starting  it.  Faults  in  these  systems  show 
themselves  only  when  an  engine  is  running. 

ENGINE  LOSES  POWER 

An  engine  will  lose  power  through  a  defect 
of  compression,  carburetion,  ignition,  cooling 
or  lubrication,  or  because  of  a  mechanical 
fault. 

If  the  trouble  comes  from  cooling  or  lubri- 
cation, the  engine  will  overheat  and  thus 
make  the  cause  known.  A  bearing  that  binds 
will  become  very  hot,  while  if  the  cooling  sys- 
tem fails,  the  engine  will  be  hot  all  over. 
When  the  engine  is  excessively  hot,  the  pis- 
tons will  expand,  and  much  of  the  power  of 


250          TRACTOR  PRINCIPLES 

the  engine  will  be  used  up  in  forcing  them  to 
move. 

An  engine  that  is  not  hotter  than  usual, 
and  is  having  regular  and  even  explosions, 
probably  loses  power  through  a  loss  of  com- 
pression. This  is  the  most  usual  cause  of 
this  trouble,  and  it  is  located  and  remedied 
as  explained  in  Chapter  XII. 

If  compression  is  good,  the  loss  of  power 
may  be  due  to  a  clogged  muffler  or  exhaust 
pipe,  which  will  not  permit  the  free  escape  of 
the  burned  gases.  This  condition  will  pre- 
vent full  charges  of  fresh  mixture  from  en- 
tering the  cylinders,  and  the  engine  then  can- 
not be  expected  to  deliver  full  power. 

Another  possible  cause  of  a  loss  of  power 
with  the  engine  apparently  in  proper  condi- 
tion is  the  sticking  or  poor  adjustment  of  the 
governor.  The  factory  adjustment  of  the 
governor  should  not  be  changed,  however, 
until  it  is  definitely  proved  that  that  is  where 
the  trouble  lies. 

If  the  engine  misses  fire,  or  runs  irregu- 


LOCATING  TROUBLE  251 

larly,  the  loss  of  power  will  be  due  to  faulty 
carburetion  or  ignition.  The  mixture  may 
be  too  rich  or  too  lean;  in  either  case  the 
trouble  will  be  remedied  by  readjusting  the 
carburetor.  A  mixture  that  is  very  much 
too  lean  will  make  itself  known  by  backfiring; 
there  will  be  little  explosions  at  the  carbu- 
retor. This  should  be  remedied  at  once,  for 
the  danger  of  fire  from  it  is  very  great. 
Black  smoke  at  the  exhaust  is  a  sign  of  a 
mixture  that  is  too  rich. 

An  engine  will  not  deliver  full  power  if  it 
is  run  on  a  retarded  spark.  A  loss  of  power 
from  this  cause  will  be  accompanied  by  gen- 
eral overheating  of  the  engine. 

ENGINE  STOPS 

The  manner  in  which  an  engine  stops  will 
indicate  the  reason  for  it. 

A  failure  of  the  ignition  system  that  stops 
the  formation  of  current,  like  the  sticking  of 
the  circuit  breaker  lever,  will  cut  off  all  ex- 
plosions instantly;  the  engine  will  stop  ab- 


252         TRACTOR  PRINCIPLES 

ruptly.  An  engine  will  not  stop  abruptly 
from  any  fault  with,  the  mixture;  with  mix- 
ture trouble  the  explosions  will  become  weak- 
er and  weaker  until  they  cease. 

If  an  engine  stops  through  a  failure  of  the 
lubrication  or  cooling  systems  it  will  be  in- 
tensely hot,  which  will  not  be  the  case  if  the 
fault  is  with  carburetion  or  ignition. 

A  running  engine  will  not  be  brought  to 
a  stop  by  a  loss  of  compression. 

ENGINE  MISSES 

A  steady  or  irregular  miss  in  one  cylinder 
is  usually  due  to  the  spark  plug's  being 
cracked  or  dirty.  Carburetor  trouble  will  af- 
fect all  the  cylinders;  it  cannot  affect  one 
cylinder  only,  and  missing  in  one  cylinder 
may  be  put  down  as  ignition  trouble.  In  this 
case  ignition  trouble  does  not  mean  magneto 
trouble,  for  if  the  magneto  produces  spark- 
ing current  for  one  cylinder  it  will  produce  it 
for  all.  Therefore  ignition  trouble  in  only 
one  cylinder  is  in  those  parts  of  the  ignition 


LOCATING  TROUBLE  253 

system  supplying  that  cylinder;  that  is,  in 
the  spark  plug  or  in  the  spark  plug  cable. 

A  less  likely  cause  for  missing  in  one  cyl- 
inder only  is  poor  compression.  It  is  usually 
the  case  that  if  compression  is  poor  in  one 
cylinder  it  is  poor  in  them  all,  but  a  broken 
valve  or  piston  ring  or  a  weak  valve  spring 
will  weaken  compression  in  one  and  not  in 
the  others. 

A  cylinder  that  misses  is  cooler  than  the 
others,  and  can  be  located  by  feeling.  It  can 
also  be  located  by  short-circuiting  the  spark 
plugs  one  at  a  time ;  this  will  make  no  differ- 
ence in  the  dead  cylinder,  but  when  the  spark 
plug  of  an  active  cylinder  is  short-circuited 
the  speed  of  the  engine  will  drop. 

To  short-circuit  a  spark  plug,  take  a 
wooden-handled  screwdriver  or  other  tool 
and  rest  the  blade  on  the  engine  near  the 
spark  plug ;  then  tilt  until  its  shank  is  close  to 
the  spark  plug  terminal.  The  spark  current 
will  then  pass  to  the  metal  of  the  engine  by 
way  of  the  tool  instead  of  by  the  spark  plug 


254          TEACTOE  PEINCIPLES 

points.  This  is  also  a  test  of  ignition,  for  a 
spark  will  pass  between  the  terminal  and  the 
tool. 

Irregular  missing  in  all  cylinders  may  be 
due  to  a  fault  at  one  of  the  parts  of  the  igni- 
tion system  that  supplies  them  all;  a  dirty 
distributor,  for  instance,  or  a  sticking  cir- 
cuit breaker  lever,  or  rough  platinum  points. 
It  may  also  be  due  to  a  clogged  fuel  line, 
which  prevents  the  carburetor  from  getting 
a  regular  and  sufficient  flow. 

Irregular  missing  will  also  be  caused  by 
loose  ignition  connections,  and  by  loose 
switch  parts. 

ENGINE  STARTS;  BUT  STOPS 

When  an  engine  starts  readily  but  quickly 
slows  down  and  stops,  the  reason  is  almost 
always  an  insufficient  supply  of  fuel.  An  ob- 
struction in  the  pipe  may  prevent  the  fuel 
from  flowing  fast  enough  to  keep  the  carbu- 
retor bowl  filled  when  the  engine  is  running; 
when  the  engine  starts,  the  fuel  is  sucked  out 


LOCATING  TROUBLE  255 

of  the  spray  nozzle  faster  than  it  comes  in 
through  the  float  valve,  so  the  carburetor  is 
soon  drained  and  the  engine  stops.  The  bowl 
then  fills,  only  to  be  sucked  dry  again  when 
the  engine  is  next  started. 

This  difficulty  is  caused  by  dirt  in  the  fuel, 
which  collects  in  the  strainer  or  the  fuel  pipe. 
The  strainer  is  so  arranged  that  it  may  be 
easily  drained  and  cleaned;  to  clear  out  the 
pipe,  shut  off  the  fuel  at  the  tank,  discon- 
nect the  pipe  at  both  ends,  and  blow  through 
it. 

The  strainer  should  be  drained  every  day ; 
it  is  sufficient  to  open  the  strainer  drain  cock 
for  two  or  three  seconds. 

Most  of  the  troubles  due  to  dirt  in  the  fuel 
will  be  avoided  if  the  fuel  is  strained  when 
filling  the  tank. 

Another  thing  that  will  bring  an  engine  to 
a  stop  is  the  clogging  of  the  vent  holes  in  the 
tank  filler  cap  and  in  the  top  of  the  carbu- 
retor bowl.  These  holes  should  be  clear,  so 
that  air  can  enter  to  replace  the  fuel  that 


256         TRACTOR  PRINCIPLES 

is  used;  if  air  cannot  enter  the  fuel  will  not 
flow,  and  the  tank  is  then  said  to  be  air-bound^ 

ENGINE  OVERHEATS 

An  engine  may  overheat  either  because  it 
produces  more  heat  than  the  cooling  system 
can  take  care  of,  or  because  the  cooling  sys- 
tem is  not  taking  off  all  of  the  heat  that  it 
should. 

Running  an  engine  with  the  spark  retarded 
will  cause  it  to  overheat ;  so  will  a  failure  of 
the  lubrication  and  an  obstruction  to  the 
passage  of  the  exhaust  gases. 

If  an  engine  has  been  taken  down  and 
overheats  when  it  is  reassembled,  it  may  be 
that  the  magneto  has  been  wrongly  timed, 
and  produces  its  spark  too  late.  If  an  engine 
has  been  running  properly  but  begins  to  over- 
heat, the  ignition  cause  will  be  the  faulty 
setting  of  the  spark  control,  or  the  slipping 
of  the  spark  control  rod. 

When  an  engine  is  run  on  kerosene,  the 
oil  in  the  crankcase  must  be  frequently 


LOCATING  TROUBLE  257 

drained  off  and  replaced  with  fresh  oil.  The 
reason  for  this  is  that  part  of  the  kerosene 
that  goes  to  the  cylinders  does  not  vaporize 
and  burn,  but  works  its  way  past  the  pistons 
and  into  the  crankcase,  where  it  thins  the 
lubricating  oil.  As  the  oil  thins,  it  loses  its 
ability  to  lubricate,  and  the  engine  begins  to 
overheat. 

Anything  that  produces  extra  friction  will 
cause  overheating,  as,  for  example,  a  wrist 
pin  that  works  endways  and  rubs  against  the 
cylinder  wall,  or  a  tight  bearing. 

For  a  cooling  system  to  work  properly  it 
must  contain  a  full  supply  of  water,  the  pas- 
sages must  be  clear,  sufficient  air  must  pass 
through  the  radiator,  and  the  pump  must  be 
in  proper  condition. 

Hose  connections  will  rot,  and  a  strip  of 
rubber  may  peel  off  the  inside  and  be  drawn 
across  the  passage ;  or  if  dirty  water  is  used, 
the  dirt  may  choke  the  fine  radiator  passages 
or  other  channels.  If  the  radiator  is  covered 


258          TRACTOR  PRINCIPLES 

with  mud,  air  cannot  get  at  the  tubes  to  take 
the  heat  from  the  water  that  they  contain. 

A  very  usual  cause  of  overheating  is  a 
slipping  fan  belt ;  an  adjustment  is  provided 
by  which  the  belt  can  be  tightened  when  it 
works  loose. 

ENGINE  SMOKES 

Black  smoke  indicates  that  the  mixture 
is  too  rich ;  blue  smoke  is  a  sign  of  too  plenti- 
ful lubrication.  Oil  that  is  too  thin,  or  that 
is  of  a  poor  grade,  will  cause  smoking;  good 
quality  oil  of  the  grade  recommended  by  the 
manufacturer  should  always  be  used. 

Broken  piston  rings,  or  rings  stuck  in  their 
grooves,  will  be  the  cause  of  smoking  because 
they  will  permit  an  excess  of  oil  to  pass  by 
them. 


CHAPTER  XIV 

CAUSES  OF  TROUBLE 

Engine  will  not  start.  No  mixture. 

No  ignition. 
No  compression. 

Engine     starts,    but  Clogged  fuel  pipe  or 
will    not    continue      strainer, 
running.  Air-bound  tank  or  car- 

buretor. 

Clogged  exhaust. 
Wet  spark  plugs. 
Governor   out   of   ad- 
justment. 

Engine  loses  power.    Retarded  spark. 

Poor  compression. 
Overheating. 
Clogged  exhaust. 
Incorrect  mixture. 
Governor   out  of  ad- 
justment. 
Tight  bearings. 
Dragging  brake. 
Slipping  clutch. 
Overloaded. 

259 


260         TRACTOR  PRINCIPLES 

Engine     stops     sud-  Ignition  trouble, 
denly. 

Engine    slows    down  Clogged  fuel  supply, 
and  stops.  Incorrect  mixture. 

Overheated. 

Regular  miss  in  one  Defective   spark  plug 
cylinder.  or  wire. 

Irregular  miss  in  all  Sticking      contact 
cylinders.  breaker. 

Defective  distributor. 
Clogged  fuel  line. 
Irregular  fuel  feed. 
Water  in  fuel. 
Faulty    ignition    con- 
nections. 

Engine    runs    un-  Incorrect    spark   plug 
evenly.  gap. 

Incorrect  mixture. 
Binding  carburetor 

float. 

Sticking  valves. 
Sticking  governor. 

Engine  overheats.        Spark  retarded. 

Faulty  cooling. 
Faulty  lubrication. 
Clogged  exhaust. 


CAUSES  OF  TROUBLE  261 

Engine  smokes.  Black  smoke;  mixture 

too  rich. 
Blue  smoke ;  too  much 

oil. 
Broken  or  stuck  pistou 

rings. 
Poor  oil. 

Engine     backfires  Mixture  too  lean, 
through      car-  Sticking  inlet  valve  or 
buretor.  weak    inlet    valve 

spring. 

Explosions     in     ex-  Missing  spark, 
haust  pipe.  Mixture  too  rich. 

Sticking     exhaust 
valve. 


INDEX 


Adjusting  a  carburetor, 
213 

Advance  of  ignition;  the- 
ory of,  18 

Air  cleaner  or  washer,  71 

Air  inlet;  extra,  63 

Armature,  106 

Atwater  -  Kent  ignition 
system,  136 

Automatic  carburetor,  63 

Automobiles  and  tractors 
compared,  1 

Axles;  types  of  front,  172 

Backfire,  55 

Balance   weights,   31 

Bearings,  31 

Bosch  magneto;  theory  of, 

110 

Bosch  magneto  circuit,  111 
Bosch    magneto    windings, 

110 

Bull  gear  drive,  165 
Burning  point  of  oil,  182 

Cam,   39 

Carbon;  formation  of,  56 
Carbonization,    56 
Carbon;  removing,  242 
Carburetor,  57 
Carburetor  action,  60 
Carburetor        adjustment, 
213 


Carburetor  adjustment  for 

two  fuels,  218 
Carburetor ;  compensating, 

63 

Carburetor  connections,  89 
Carburetor;        description 

of,  72 

Carburetor;  float  feed,  76 
Carburetor ;     heating    the, 

70 

Carburetor;  parts  of,  70 
Carburetor;  pump  feed,  80 
Carburetor;    stopping    on 

gasoline,  218 
Carburetor  strainer,  89 
Carburetor;    trouble   with, 

215 
Carburetor;  using  water  in, 

219 

Causes  of  trouble,  259 
Centrifugal  force,   94 
Change  speed  gear;  action 

of,  152 
Change    speed    gear;    jaw 

clutch,  156 

Change  speed   gear;   pur- 
pose of,  6 

Change  speed  gear;  shift- 
ing, 203 

Change  speed   gear;   slid- 
ing, 154 

Change  speed  gear;  theory 
of,  149 


268 


264 


INDEX 


Choke,  67 

Circuit;    Bosch    magneto. 

Ill 
Circuit   breaker;  magneto, 

110 

Cleaner;  air,  91 
Clutch;   action  of,  144 
Clutch;  expanding,  145 
Clutch;  how  to  use,  205 
Clutch;  plate  or  disk,  146 
Clutch;  purpose  of,  6 
Cold  weather  care  of  trac- 
tor, 207 

Cold  weather  starting,  207 
Combustion  space,  11 
Combustion;  theory  of,  52 
Compression ;     importance 

of,  16 

Compression   leaks;   locat- 
ing, 228 

Compression  stroke,  16 
Compression;  testing  the, 

227 

Connecting  rod,  35 
Cooling  system,  46 
Crank  shaft,  30 
Cycle;  gas  engine,  11 


Dead  strokes,  12 
Differential;  action  of,  161 
Differential ;  purpose  of,  7 
Differential;  theory  of,  158 
Dirt  in  the  fuel,  215 
Disk  clutch,  146 
Distributor;  magneto,  124 
Dixie  magneto  action,  119 
Double    bowl    carburetor ; 

adjustment  of,  218 
Double  opposed  engine,  25 


Drive;  master  gear  or  bull 

gear,  165 

Drive;  purpose  of,  6 
Drive;  worm,  166 


Engine  base,  30 

Engine;  double  opposed, 
25 

Engine;  horizontal,  25 

Engine;  how  power  is  de- 
livered by,  21 

Engine  loses  power,  249 

Engine  misses,  252 

Engine  overheats,  256 

Engine;   priming,  214 

Engine;  principle  of,  9 

Engine;  purpose  of,  6 

Engine  smokes,  258 

Engine  starts;  but  stops, 
254 

Engine  stops,  251 

Engine  trouble;  locating, 
246 

Engine;  vertical,  25 

Engine  will  not  start,  246 

Exhaust  stroke,  20 

Exhaust  valve,  38 

Expanding  clutch,  145 

Extra  air  inlet,  63 

Firing  order,  28 

Float   feed   carburetor,  7(5 

Force  feed   oiling  system, 

186 

Frame;  purpose  of,  8 
Freezing;  to  prevent,  209 
Front  axles;  types  of,  172 
Fuel;  dirt  in  the,  215 
Fuel;   straining  the,  89 


INDEX 


265 


Gas  engine  cycle,  11 
Gasket,  30 
Gasoline  mixture,  57 
Governor,  94 
Grease  cup,  197 
Grease;  when  used,  182 
Grinding  valves,  229 
Grounded  circuit  or  ground 
return,  125 

Heat;  action  of,  9 
Heat;  effect  on  oil  of,  177 
Heat  necessary  in  forming 

mixture,  58 

Heating  the  carburetor,  70 
Heating  the  mixture,  86 
Horizontal  engine,  25 

Ignition  point ;  changing 
the,  103 

Ignition  system;  Atwater- 
Kent,  136 

Ignition  system;  parts  of, 
105 

Ignition;  theory  of,  17, 
102 

Impulse  starter,  128 

Induction  and  induced  cur- 
rent, 106 

Inductor  magneto,  115 

Inlet  stroke,  14 

Inlet  valve,  38 

Jack  shaft,  165 
Jaw   clutch   change   speed 
gear,  156 

K-W  magneto  action,  115 
Kerosene  mixture,  57 


Leaks  of  compression;  lo- 
cating, 228 

Lean  mixture,  54 

Loading,  67 

Lubricating  systems,  184 

Lubrication  chart;  use  of, 
182 

Lubrication ;  importance 
of,  175 

Magnetism,  105 
Magnet;  poles  of,  106 
Magneto  action ;  Bosch,  110 
Magneto  action ;  Dixie,  119 
Magneto  action;  K-W,  115 
Magneto   distributor,  124 
Magneto      distributor ; 

cleaning,  222 
Magneto  inductor,  115 
Magneto;  oiling  a,  221 
Magneto  platinum  points; 

care  of,  221 
Magneto  safety  spark  gap, 

127 
Magneto  spark;  theory  of, 

105 
Magneto;  theory  of  Bosch, 

110 
Magneto   timer   or  circuit 

breaker,  110 
Magneto  timing,  223 
Magneto    trouble;    testing 

for,  224 
Manifold,  70 
Master  gear  drive,  165 
Mechanical  oiler,  192 
Mixer,  57 

Mixing  chamber,  70 
Mixture  changes  with  en- 
gine speed,  62 


266 


INDEX 


Mixture;  formation  of,  53 
Mixture ;       gasoline       and 

kerosene,  57 

Mixture;  heating  the,  86 
Mixture;  heat  necessary  to 

form,  58 
Mixture;  rich,  55 
Mixture;  theory  of,  9 
Mixture;  thin,  or  lean,  54 

Oil  affected  by  heat,  177 
Oil;     burning    point    and 

viscosity,  182 
Oil  cup,  193 
Oiler;  mechanical,  192 
Oiling  chart;  use  of,  182 
Oiling;  importance  of,  175 
Oiling  systems,  184 
Oil  pump,  188 
Oil;  varieties  used  on  trac- 
tors, 179 

Piston,  34 

Piston  pin,  34 

Piston  rings,  37 

Piston  rings;  care  of,  228 

Plate  clutch,  146 

Poles  of  magnet,  106 

Power  diagram,  21 

Power  production,  12 

Power  stroke,  19 

Preignition,  56,  83,  104 

Priming  the  engine,  214 

Pump  feed  carburetor,  80 

Push  rod,  42 

Push  rod  adjustment,  234 

Radiator,  48 

Retard  of  ignition;  theory 
of.  19 


Rich  mixture,  55 
Rocker  arm,  42 


Safety  spark  gap,  127 
Shuttle  armature,  107 
Sliding  change  speed  gear, 

154 
Spark   coil;    principle    of, 

133 

Spark   coil;    vibrator,   138 
Spark    coil;    windings    of, 

134 

Spark  plug,  140 
Spark  plug  gap,  226 
Spark  plugs;  trouble  with, 

225 

Splash   oiling  system,  184 
Spray  nozzle,  57 
Spring  support,  173 
Starter;  impulse,  128 
Starting   in    cold   weather, 

207 

Starting   the    engine;    the- 
ory of,  13 
Steering  gear;  purpose  of, 

7 
Steering;     instruction     in, 

205 

Storing  a  tractor,  21§ 
Straining  the  fuel,  89 
Strangler,  69 


Tappet,  42 

Tappet  adjustment,  234 

Temperature ;      effect      of 

changes   on   mixture,   66 
Testing     for     magneto 

trouble,  224 


INDEX 


267 


Testing    the    compression, 

227 

Theory  of  gas  engine,  9 
Thermo-syphon  cooling 

system,  48 
Thin  mixture,  54 
Throttle,  68 

Throws  of  cranK  shaft,  30 
Timer;  magneto,  110,  121, 

122 

Timing  a  magneto,  223 
Timing  the  valves,  237 
Tractor;  caring  for  in  cold 

weather,  207 

Tractor;  difficulties  in  oil- 
ing, 178 

Tractor  driving,  205 
Tractor;   handling   a  new, 

201 

Tractor  inspection,  203 
Tractors  and  automobiles 

compared,  1 
Tractor;  storing,  210 
Tractor  types,  167 
Transmission ;     parts     of, 

143 


Trouble;  causes  of,  259 
Trouble;  locating,  246 

Valve;  exhaust,  38 
Valve  grinding,  229 
Valve;  inlet,  38 
Valve  mechanism,  42 
Valve  operation,  39 
Valve     seat;     redressing, 

234 

Valve  timing,  237 
Vertical  engine,  25 
Vibrator  coil,  138 
Viscosity  of  oil,  182 

Washer;  air,  91 

Water    added   to   mixture, 

58,  83,  219 
Water  jackets,  48 
Windings;  Bosch  magneto, 

110 
Windings    of    spark    coil, 

134 

Worm  drive,  166 
Wrist  pin,  34 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

RENEWED  BOOKS  ARE  SUBJECT  TO  IMMEDIATE 
RECALL 


DEC  20  -82 

on  is  ' 


LIBRARY,  UNIVERSITY  OF  CALIFORNIA,  DAVIS 

Book  Slip-50m-12,'64(F772s4)458 


361398 


Whitman,  R.B. 

Tractor  principles 
PHYSICAL 
SCIENCES 
LIBRARY 


TL233 


